Building a beginner trial bike I'm slowly turning my XC biking time into trial sessions. For now I'm only doing some track stands, endo's and wheelies, but I'm probably going to go for more as soon as I can do these properly. I'm probably never going to reach the level of Danny Macaskill, but that's for sure the kind of stuff I want to do.

I currently have a good, trustworthy mountain bike. And I'm using it for this basic trial. Alas, I'm afraid I could badly damage it, as my wheelies landing are not as smooth as they should be, and so are my endo's. I need this bike to go to work, and it really has a high sentimental value, so I can't afford to break it.

I'd have a few questions related to this.


Is there a (non-obvious) risk I could badly damage the fork or frame of my bike by doing some badly executed trial figures? I know for a fact that my front wheel hub is already bent. How about the wheel slots?
Should I decide to go for a specialised trial bike, what kind of gear should I get? I've seen some low-profile hard tail frames, they seem essential. What kind of wheel should I take (size ?), etc.
Again, if I'm making a new bike, I'd like to keep a reasonable budget. What are the parts that must be of good quality, and what are these who can start "small" to be improved later if needs be?
Would rim brakes be sufficient for starters, or do I absolutely need huge and expensive disk brakes to start?


Thanks for your help. Don't hesitate to be verbose: I might have been riding for a while, it's really this year that I started maintaining my bike myself.
Perhaps you'll have more luck with answers on specialised trials forums, like http://www.trials-forum.co.uk/. However, I'll try to address your questions briefly. 


Risk to damage the fork/frame? Yes, absolutely. But all depend on what you are doing and what bike it is. I've snapped a few frames doing trials and stunts. But chances of damaging are less if you are using trials frame.
Wheel size is a great debate in a trials world. There are 26", 24" and 20" (19") wheels. All down to the preference and rider level. I'd start with 26" and then once you know what you want/need, decide on the sizes. If you are very keen on trials and have finance, definitely get a trials bike. Many times while learning I found my bike stopping my progress. 
Good quality parts... get a good chain and good freewheel. Because if freewheel slips while doing gaps - you are going down. And that can lead to an injury. Also get a great rear tyre with good brake. A lot depends on that. Other parts are essential, but these are high priority.
Breaks are another point of debate in trials world. Magura HS33 - hydraulic rim brakes used to be very popular 10 years ago. Now I'm not quite sure about the trends. Certainly I'd put some cash in for a good rear break - that is a vital part of the bike.


A lot of your questions are down to experience. You'll know when you need a better rear break and what other parts to change. And you'll slowly assemble a great bike, going along with your skill level. 

And good luck!