Okay, let's take it one at a time.
The correct bowl number is C474CEFG, not "CT"474. ST is the tank. C is the bowl. Put them together and you get CST (or a two-piece toilet). That said, some suppliers DO list the bowl as "CT". Go figure. It's wrong, but they do it.
What Toto is recommending is that you install a skirted Vespin II bowl rather than a Drake II bowl. The Vespin II is installed using Toto's Unifit Adapter. The bowl comes with a 12" adapter. You would buy the C474CEFG bowl and the 10" Unifit Adapter, which is model number TSU01W.10 and which is sold separately. Here are the installation instructions with the Unifit.http://www.totousa.com/Portals/0/Pro..._TOILET_IM.pdf
The Drake II and the Vespin II use the very same tank; in fact if you look on the box it will say "Drake II/Vespin II Tank" on it -- ST454E. So all you would have to do is buy the bowl and adapter and you'd be in business.
Yes, the Vespin II flushes about the same as the Drake II. It's intended to be a skirted version of the Drake II. We have a Carlyle II, which is a skirted Ultramax II, and love it. Doubtless the $350-ish you spend on the new bowl will be less than a plumber would want to move the flange. I think. If you can exchange the Drake II bowl for the Vespin II bowl for a small charge, that's even better, and the best way to go, no question about it.
As far as the level of the flange, when you go to install the new toilets, no big deal. Just use two wax rings instead of one. You stack them, either two plain wax rings, or one with a funnel in it on top of one without a funnel, but never two with a funnel. Or use an extra-thick #10 wax ring.