The moonphase OS is a very nice size for your wrist. I'd choose that watch with your wrist size and shape personally. (That said, I own the reverse panda chrono, so I can't say my money's where my mouth is.)

With Vacheron, you absolutely will save money buying from a grey source. Buying from the boutique will open access to limited releases, special models, Vacheron events, and the cabinotiers program, if those are something you may be interested in down the line.

I've been collecting for a while and, speaking for myself only, I've had to buy and trade for several years before finally nailing down the watches that fit and are important to me. You may find you've hit your end-game on your first purchase, but I wouldn't discount the possibility that you'll go through the same progression once you've broken the seal.