To get started just grab a pair of recievers( or just a lower if you are buying the upper complete. Which can be a good plan depending.)
Troy TRX is the round free float tube correct? I have the MI SS model and the thing is great... put the rails where you want them. If you don't have accessories to mount you have a very comfortable free float tube. Flexibility.
Varmint barrel can be had in 16" or 18" if you prefer. Wylde chamber seems to be what people use for varmint guns.
Fixed stock, just get a A2. Cheaper than the magpul stuff and it's solid. I'd say fixed for any rifle you are putting a scope on. CTR, UBR... I havent tried these yet but they do get good reviews as far as being solid goes. If you want to drop the cash go for it.
Trigger! Get a nice one. I have a RRA 2 stage. Might be able to find something better out there though. Maybe someone else has experiences with other triggers.
Pick your optic and you are away.
Edit: realize now that this is an old thread. But I typed it up so it's here now.