Campy shopping list

OK, ya'll, help me out. I have decided to put Campy stuff on my "new" colnago frame, and have decided to go with either the Chorus or Record ( my SO has Chorus and says it is great, works fine, yada de yada, I think that the price difference isn't THAT much to upgrade to the 10 speed Record).
The bike already has an It BB, threadless headset, and seatpost, so I can knock those off the list. But I am worried about compatibility problems if I buy each part separately?
So I think I am going to order a groupset, either Chorus or Record (someone talk me off the ledge here) to avoid the first time builder problem of buying two parts that don't work together. Is there anything I need to consider besides the obvious (crank arm length, chainring sizes)? Do I want a braze-on or clamp on FD?
Thanks again for everyone's help...

Unless you are uber rich, or big time racer (an elite rider), go with Chorus and save $$. Thought the price difference was still pretty big to me.

Braze on or clamp on for the FD? I would imagine that yuor Colnago comes with braze-on. so not much choice there. I don't think you get a choice. Its one or the other cause the frame will dictate it. Now if your bike does not have a braze-on, then you could get an adapter/collar and use a braze-on FD.

If you want to keep the BB that came on the bike, you'll need the older square-taper cranks. The newer Ultra-Torque cranks don't need a traditional BB - they use 'cups' that screw into the BB.

Some of the groups I have looked at come with a BB...is it worth replacing the older BB that is on there with a new one? I know I need the IT BB but if it is just a matter of getting the square type crank, nothing else, I will keep the one that is one there, if it is going to throw everything else off, I will replace it?