I'm in club Intellijel... Lycans rules!
Building in a small case is akin to going from building grandfather clocks to wristwatches. The amount of knowledge and precision becomes of the utmost importance. Getting the most mileage out of a handful of modules requires this knowledge and experience. Getting a small rack correct the first time around without experience is going to be a tough task.
Ambient tracks produced via modular generally have lots of modulation involved... some blatant and a lot is very subtle. There's going to be lots of small modulation in order to keep the sound fresh and evolving. Listening to one plain oscillator drone on... not very entertaining.
People are enticed to start with a small rack because it's less expensive to put together. But if it can't do what you're hoping it will do, you're throwing your money away.
+1 on VCV rack. That's what I started on (even though I've been into synthesizers for about 30 years). If you can build the sort of ambient patches you like in VCV Rack, you can translate all of those virtual modules into a shopping list for real world modules. VCV Rack is FREE. It does have some paid modules available. But nothing that's a show-stopper if you don't have it. Get in some virtual time before you spend thousands of dollars on real world equipment. Your bank account will thank you.