I would humbly like to point out that there is nothing odd about using a low pass gate with a complex oscillator. This is literally one of the main building blocks of west coast style synthesis. I own an Erica Synths Pico System III, and despite it being a compact "higher end of low-budget" synth, it also has two very enjoyable resonant low pass gates that I have found almost irreplacable. I don't know how similar they are to the Black LPG in terms of sound, but they seem similar in function. You should definitely look into multiple types of filter and LPG (including filters that feature a VCA and a filter but offer separate controls, which sounds like it may be something you're into), but the one you have now is theoretically perfectly fine since the complex oscillator offers a variety of timbrial variation options outside of subtractive filtering, and the Erica Synths module does that subtractive filtering anyway.
I agree that two attenuverter modules taking up much space is a lot. One module to consider here is the Happy Nerding 3xMIA, which is very similar to the 321 from Frap Tools except that it has two inputs for each channel, allowing you to either plug two signals in and mix them as well as invert and attenuate them, but still lets you do offsets with any channel that doesn't have a cable plugged in. I had a Frap Tools 321 and while I think it works good, the knobs aren't as fun as they could be and I found I often forgot what was what in terms of the more esoteric functions. The 3xMIA solved both of these things for me. Definitely keep an eye out for other options, though.
Your Befaco Rampage can be patched to be an ADSR, in addition to being two independent AR generators. If you clear out the Black CV Tools, you will have plenty of room to look at a dedicated envelope generator (or even a Mutable Peaks clone with lots of different options to play around with in 4-8 hp - highly recommended as something to look at). However, don't forget that part of the fun of a Rampage or a Maths or a similar Serge type module is that it can do lots of different jobs as long as you don't necessarily need them all at once. When I got my Maths I went through a big list I found of functions and patches for mine to get familiar, and it really keeps me from constantly drooling over modules that do stuff I already have in some form (or makes me more determined to get them once I find I can't get it quite how I want on the function generator).
Your plan works good. My plan might work good. Someone else's plan might work good. Right now, I think going for a filter/lpg and the Rampage next would give you a fully functioning small setup that you could learn a surprising amount of modular basics on and have fun doing so. From there, determining your next move will be much easier, especially if you combine this with researching the different classic module types everyone says you need and figuring out which ones work the best.
