Unfortunately, Dreadknights are Inquisition Space Marine only, so they would be of Unique Rarity, and require the Peer (Adeptus Astartes) and Peer (Inquisition) talents to be available.  You'd probably also have to modify it to accept a slimmed down sentinel instead of a set of power armor in the pilot's position as well, unless you wanted to get a set of Astartes power armor to fit inside as well.<br/><br/>As for getting a Titan, you'll mostly need to get through the line at the Bureau of Bureaucracy, then get a spare cruiser with most of the hull space dedicated to cargo to carry it in.  Titans are only supposed to be piloted by special people with psychic talent and an intimate link to the machine spirit of the titan, but you can probably find a way around having to get your synch ratio up to pilot the damned thing.<br/><br/>The Imperial Titans, according to the fluff, are absolutely vital in securing planets for the Imperial guard.  Basically, the Space Marines do most of the offensive work, the Titan Legions handle the rearguard actions, and the Imperial Guard fill all the spaces in between.  The PDF auxileries are there as redshirts to make the Imperial Guard look almost competent, and low intensity campaigns are usually conducted solely by the Imperial Navy, often with the help of a Rogue Trader or two.  As a Rogue Trader ship, you're entitled to any Imperial asset that leaves Imperial space, though a major official such as an Inquisitor or other major throne agent can take away that authority.  (Most Naval assets, for example, won't be permitted to you because they're the property of the sector Admiral, who outranks a rogue trader even outside the Imperium.)<br/><br/><br/>Here's the list of assets a rogue trader can typically acquire:<br/><br/>PDF: Your basic, run of the mill planetary defense force, usually armed with mostly functioning lasguns and a really low intensity training program.  If you get lucky, the planet will have existing martial traditions, and the PDF will be armed with low tech weapons they actually know how to use.  If you get unlucky, the PDF will come from some noble's private historical reenactment planet, and be armed with feudal era weapons that they're not even sure how to operate.  PDFs are almost universally wretched military units, because if they could beat the Imperial Guard, their home planet would be able to rebel against the Imperium.  Therefore, PDFs which overcome a certain threshold of military efficiency are usually promoted to Imperial Guard regiments or targeted for destruction by the Inquisition.<br/><br/>Imperial Guard: Imperial guard regiments are remarkably self sufficient military units, though getting the services of one is difficult for a Rogue Trader.  Each regiment consists of approxomately 10,000 soldiers and support personell, and is usually speciaized for a particular function.  The guard will usually not want to transport a military unit smaller than a regiment, and for planetary scale operations, prefers to combine 3-4 regiments into a division.  If major resistance is expected, the guard will want to bring about 4-10 divisions to pacify the planet, relying heavily on numerical superiority to win.  Elite squads such as Storm Troopers and Grenadiers can be more easily added to the crew of a Rogue Trader's ship for greater efficiency in boarding actions, and Regiments are usually willing to sell surplus military hardware in times of relative peace, since they often keep many spares available.<br/><br/>Space Marines: The space marines operate with independence roughly equal to that of Rogue Traders, with power centralized in the chapter master just as the Rogue Trader holds the power in his crew.  Given suffcient cause, Space Marines are usually perfectly willing to provide a squad of marines to a Rogue Trader crew, as long as the chapter and the crew have common goals.  In more dire circumstances, a Marine chapter might commit an entire company of Marines and a strike cruiser to pacify a particularly stubborn threat.  If an entire Marine chapter can be roused, they will usually field a fleet of 1-2 battle barge battleships, 4-8 strike cruisers, and around 6-20 escort vessels, depending on the space inventory of the chapter; spaceborne chapters will have more ships, while some chapters have no spaceships at all, and must rely on external vessels for transport, though they usually can call upon the Master of the Forge to equip any vessel they travel on with boarding torpedoes and modify carriers to carry Thunderhawks or drop pods to aid in planetary assaults.<br/><br/>Titan Legions: The titan legions are an elite group of mech pilots tightly controled by the administratum in segmentum solar.  They travel the stars in vast Titan Arks which are battleship sized transport vessels which carry 3-12 titans for battle.  Getting a titan to a planet and landing it usually requires a massive level of space and ground security, so Titans are most often fielded either in defensive operations, or as a last resort in a particularly complex combat unloading operation.  A titan can utterly crush most planetary armies, and has void shields to prevent it from being easily destroyed in air attacks and planetary bombardment.  Elite infantry can disable a Titan reasonably easily by boarding it and then killing the crew from the inside, but such efforts are easier said than done.  Chaos, Orks, Eldar, and the Tyranids each have their own equivelents of Titans, while the Tau have large scale atmosphere capable gunships which perform a similar role.  The deployment of titans in groups is vitally important, but a particularly large transport ship might be able to get a single Titan loaded.  The paperwork to acquire such a device would be insane, but once deployed, it would likely dominate the kind of battles Rogue Traders typcally engage in.<br/><br/>Crusaders: With the aid of the ecclesiarchy, vast armies of religious fanatics can typically be procured quite easily.  Fanatics usually provide their own ships, and are often provided with weapons upon their exit from the home sector.  Unfortunately, crusader forces are usually poorly armored, hard to control, and unwilling to spare anything that gets in their way, usually leading to such armies going splat against any reasonably hard target.  Crusades can be bolstered considerably by the addition of Adeptus Soriatas, who are skilled at leading and focusing vast mobs of fanatics for good, as well as being an elite unit.  Soriatas share many things in common with space marines, though they're considerably less tough, and have a reputation for accomplishing thier objective with 100% casualties.<br/><br/>Grey Knights: Grey Knights are the secret warriors of the Imperium, and if you know how to find them, they can kill whatever you point them at easily.  However, once the arrival of the Grey Knights is justified, the Knights themselves have unlimited authority to do with the mission area as they please, up to and including exterminatus.  Grey Knight warships include vast amounts of archeotech and xenotech, enabling them to move at incredible speeds, and deploy their higher than average yields of cyclonic torpedoes and virus bombs even through massive fleets of enemy ships.  A Forbidden Lore (Inquisition) skill of +10 or higher is needed to know of the existance of the Grey Knights.  Anyone aware of the Grey Knights is also aware of the many dark rumors about them, including that the chapter master of the group lives in the warp, interacting with demons, and that they are deeply corrupted by chaos and arcane xenotech in strange configurations.<br/><br/>Xeno Mercenaries: Outside the Imperium, it is perfectly appropriate for a Rogue Trader to hire xenos as auxileries, if he or she determines it is neccisary and in the interests of Humanity.  (Within the Imperium, alliances with the Eldar are permitted under special circumstances, but only by the order of a high ranking sector official; something which occasionally confuses planetary governors into making extremely bad decisions)  Xeno mercenaries are usually highly unreliable, but skilled in some aspect of combat that can be tactically useful.  Kroot, for example, are masters of ambush warfare and reasonably capable close combatants, making them useful against enemies that like to fight in skirmish formations, but extremely useless against forces that use static defense doctrines.  By contrast, the Orks will quickly make short work of any static defenses, with a combination of brutal firepower, Kommandos, and ded `ard charges, but can be easily broken by opponents that make use of snipers or mobility based tactics.