Replacement parts for Trek 7.3 My bicycle was stripped of parts (both wheels, seat post and saddle) outside my house and I'd like to replace them myself as the shop is looking for a huge sum of money to do it. 

This isn't the exact site I bought it off as the original ad was taken down:

http://www.littlesportbikes.ie/product/7-3-fx-trek/

I have found the following so far but I'm not sure if they will fit.

Rear Hub - https://www.amazon.co.uk/SHIMANO-FH-RM30-wheel-quick-release/dp/B00443F5ZO/ref=sr_1_3?ie=UTF8&amp;qid=1482231615&amp;sr=8-3&amp;keywords=Shimano+RM30

Skewer - https://www.amazon.co.uk/Shimano-RM30-Schnellspanne-Quick-Release-Silver/dp/B008E4K9V4/ref=sr_1_2?ie=UTF8&amp;qid=1482231678&amp;sr=8-2&amp;keywords=RM30+quick+release

Cassette - https://www.amazon.co.uk/Shimano-11-32-HG50-Speed-Cassette/dp/B001QWEOVM/ref=sr_1_1?ie=UTF8&amp;qid=1482231748&amp;sr=8-1&amp;keywords=Shimano%2C+9-speed%3A+11-32

Seat Post - https://www.amazon.co.uk/d/Sports-Outdoors/Truvativ-Hussefelt-Single-Seatpost-Offset/B004YIDSS0/ref=sr_1_4?ie=UTF8&amp;qid=1482232932&amp;sr=8-4&amp;keywords=27.2mm%2B20mm%2Boffset&amp;th=1&amp;psc=1


I'm not sure of a replacement for the front hub, saddle, skewers ans wheels. I have replacement tyre's already (x2 schwalbe marathons)

Does anybody know if these parts will fit and what alternatives I can use for the unlisted parts?
Sorry your stuff got stolen :/. 

For wheels you need basically any hybrid rim brake wheelset with standard 135mm spacing and an 8/9/10 speed rear hub. That's most non-disc hybrid wheels out there that you'll find, as well as disc sets with non-disc-specific rims. Good deals on sets can be often be had online and at shops; that's generally what you should look for if you're trying to save money. For example, here in the US when I'm working with someone in your situation, the first thing I do is look at sets on sale at the major wheel wholesalers. There's a backstory there; that whole side of the industry has a fascination with getting complete wheelset sales, and they often overproduce and wind up slashing prices later.

The hub you link to is one such compatible hub of many. For the cassette, that one is a drop-in replacement for the original one, or you could take the opportunity to go to a lower or higher low gear if you wanted. (You could go to 11-34 with your derailers and cranks, but you may need a longer chain. But, a new chain is a good idea with a new cassette anyway to avoid skipping and premature wear.) That post should also be a drop in replacement for what came on the bike.