You're not likely to find a 32T cog on a Campy cassette. 29 is as low as they go. I built my Mercian with a mix of Centaur and non-carbon Chorus. I'm not a fan of carbon fiber components on a classic bike like a Mercian and it's getting harder to avoid on the higher end groups. My suggestion is to get a Centaur or Veloce group and be done with it. Skip the lame AC-S and AC-H bottom bracket though.
If your bike was designed with room for fenders, you might need long reach brakes. If so, Campy won't work without a drop bolt. Shimano and Tektro both make some nice long reach calipers.
If you get a Campy chain, use a Wipperman connex link instead of the special tool and closure from Campy. Or just use a Wipperman chain.
Unless you are very patient, it's usually cheaper to buy parts as a group or a build kit. Unfortunately if you get brakes that don't fit or something, you might need eBay what doesn't work.
The other issue that might give you trouble is the front derailleur. You might have trouble finding anything in a 28.6mm clamp. They're out there, but getting harder to find.
While it is possible do some mixing of Shimano and Campy drivetrain components, it's probably not something you want to do without a very good reason, especially with your time constraints.