Dude! A modular synth is not a Prophet V, hello???!!! LOL, just kidding.
I've got a few modular formats in three 19" racks. Mostly large format, most of which is dotcom. Large format modules are mounted in dotcom rack frames and MOTM-compatible rack rails. I admire the walnut cabinets, but racks work better for a multi-format system, in my opinion. Not as pretty, though.
The big dotcom cabinets are very nice. I recall reading posts to the effect that overseas shipping and import fees are so high that it makes more sense to get cabinets made locally. Or is it that they don't even ship them overseas because the costs would be so high? I forget, sorry! Those cabinets are rather large, so a shipping crate has to be even larger, so the whole bundle is heavy.
Another alternative is the relatively new Box 11 System from Synthesizers.com. It's cool in a Buchla-flattering kind of way, and it looks like it would ship in compact form. (BTW, have you seen the new dotcom modular keyboard?)
In the US, dotcom modules are probably the most economical of the large formats. Elsewhere, your mileage may vary. Plus, there are compatible modules from other makers. Among other modules, STG Soundlabs (also US-based) makes a few different filters that complement the dotcom line. (Disclaimer: I am a friend of STG. By the way, STG uses dotcom VCOs in his personal modular.)
I haven't tried COTK or Moon. I have MOTM-format modules from Synthtech (MOTM), Encore, and a couple of DIY things, plus a few rack rows of Frac and Euro. A Frankensynth isn't for everyone, I know.
About half of my modules were purchased second hand. If you're not in a hurry, it's a good way to go. Dotcom modules are well-made, so dirty/scratchy pots are one of the main risks. I haven't had any issues.
If you want a large format modular system, I can recommend Synthesizers.com. It's a great foundation for a mixed system, and it's a broad enough line to stand alone. It's especially suited to the East Coast and Berlin schools, and obviously not so much to the West Coast style.
A comment on LFOs: People, including me, have openly called for a more compact LFO module from S.com. Roger Arrick isn't budging. His philosophy is that fully-featured VCOs make better LFOs, and he's right! I often use VCOs as LFOs. I love using voltage control on the "LFO", as well as hard sync, and it's great to have so many waveforms available at once. But, I also have a MOTM dual LFO module, because sometimes you reallllly only need a dumb LFO -- say, for a clock -- and the MOTM-390 has two in a single width module (one with voltage control). If I had nothing but dotcom Q106s (plus some Q141s and maybe some Q161s if there was enough room), I'd be quite happy. But, I would have fewer modules in my rack. Life's full of tradeoffs, no?
I'm currently at around 80U of modules, and it all started with a small dotcom Entry System -- it's a Gateway Drug.