Well, if money's a major issue here, I would suggest that your first move should be to replace all of that Endorphin.es stuff. It's spendy, and you can get the same things (if not better!) for less money. Kinda big, too...for example, the Furthurrr Gen is $779 and 30 hp. OR...Tiptop's Buchla 258, which is $200, and if you miss the waveshaper, you can add the Dannysound Timbre, which is based on the Buchla 259's waveshaping circuitry for another $100 and change. But not only does that save money, it saves space...the 258 is 18 hp, and the waveshaper is only 6, and that leaves a new 6 hp space to add something else.
Since you've been out of the game for a while, these days things are all about trying for maximum functionality with best-case $$$ outlays while NOT wrecking the ergonomics. It's very doable, but this isn't like whipping up some basic gear anymore. There's so many choices that you've sort of got to sort out what you want the build to DO before coming up with a build plan.
One other thing...drum machines in modular are HELLA expensive. You can do them, sure...but remember, you need the voicing AND its sequencer. Now, the Queen of Pentacles is $669 for starters, and you're still looking at outlay for a suitable pattern sequencer on top of that. So...$1k tends to be around the spot most of these come in at, and that's just not tenable when you can get a decent (and very 909-ish) machine like Uli's RD-9 for perhaps a THIRD of that. And yes, it'll lock right up to whatever sync the modular's using. Oh, and you get back another 30 hp for use elsewhere in the build. In short: if an answer exists outside of modular, it's often better to take THAT instead of using hp and cash to make it happen in the cab.