In your vintage Chorus is as nice as it gets mechanically except for later 10 speed dual pivot brakes where Campagnolo stopped using ball bearings below Record. Record adds titanium, more carbon fiber, and cosmetic flourishes - I ride Record Titanium for the hardware matching my Ti frame and sexiest skewers ever made. Going down market you loose little function (rear derailleurs mount the cage with a C-clip not the Chorus/Record bolt which is less fiddly when you take them apart to clean out the gunk) but gain weight (Centaur/Daytona generally only has the last two cogs on a carrier, not the big 2-3 pairs depending on starting cassette; Veloce has none).

Lay in a supply of right G-springs and carriers. With ADHD shifting I went through springs every few years and replaced broken carriers every two spring swaps. Re-taping the handle bars is the hardest part of the rebuild process. Shifting gets soft before the indexing mechanism won't stay in gear - pay attention and be proactive about replacement.

All the front derailleurs changed geometry in 2007 with "Quick Shift"; although the worst that will happen on a mismatch is one click more on the move between rings.

Your left shifter will run a triple derailleur using 7 of 12 clicks. That can give you lower gears (a 74mm BCD crank will run an inner ring down to 24 teeth, with 24x25 like 34x36) and/or tighter spacing over the same range - 53-39-26 x 13-14-15-16-17-18-19-21-23-26 has a lower gear than 50-34x12-13-15-17-19-21-23-25-28-32 and no gaps between the 15/17 and 17/19 cogs.

You can spend as little or much as you want on that - selling your old derailleurs and crank and buying aluminum parts not marked Record you'll pocket some money, with careful shopping you could buy used alloy derailleurs and crank for less than the price of a new Campagnlo 12-30 from the UK, buying NOS Record Titanium triple derailleurs (I just paid $220 for one from Velomine) and a Lightning crank (about $700 without rings) you'll spend over $1000.

If you want to stick with the compact Campagnolo larger cassette options include

13-14-15-16-17-19-21-23-26-29
12-13-14-15-17-19-21-24-27-30

I and others think loosing the 12 tooth cog is better than accepting another gap in the middle - I used a 50x13 big gear for the decade I spent in Colorado after moving on from 52-42 with a six cog free wheel.

IRD has a 12-32.

Buying new you MUST import your parts from Europe unless you're feeling charitable and care to send your LBS owners' children to college. Note that you don't pay VAT (20%) and shipping from Ribble Cycles in the UK is about as fast as between the coasts within the US.

As of 2010 officially the short cage rear derailleur (55mm betweeen pulleys) was good for doubles (standard 53/39 and compact 50/34) with all cogs (through 12-25 and 13-26) except 13-29 although there's some latitude depending on your hanger geometry.

The medium (72.5mm) was officially for doubles with all cogs and triples all cogs (through 12-25 and 13-26) except 13-29; long (89mm) for triples and any cogs.

12-27 and 12-30 10 cogs are recent additions for which I don't have the recommendation.

The previous Racing-T derailleurs were mediums when the biggest cassette outside the short lived mountain bike range was a 13-28 (8 or 9 cogs). The long is really long.

Campagnolo chains wear longer than others measured according to a ruler, although Campagnolo suggests measuring between rollers with calipers. KMC offers a Campagnolo specific missing link ($2-$3 each when you buy a full card of six) so you don't need to use Campagnolo's one-shot pins. The width of inner links varies between brands so you want the right master link.