First thing... don't spend any money. There's no way to casually put together a rig and get something useful unless you get extremely lucky.
Second, go to https://vcvrack.com and download the FREE modular synthesizer software. There are virtual modules that you can pay for. But the vast majority of them are free.
Do you know what a VCO is?
Do you know what a VCA is?
Do you know what a VCF is?
Do you know what an EG is?
Do you know what a SEQUENCER is?
Can you make a simple monophonic synth out of that in VCV rack? Next make the same patch with an LFO modulating the cut-off frequency filter?
Keep experimenting with VCV rack. Watch beginners' tutorials on Youtube regarding Eurorack modular. Get proficient with VCV Rack. You can make ambient patches with VCV Rack as well. Almost all of the modules have equivalents in the real world. So you're not wasting time.
At this point you've still spent ZERO money.
Once you're comfortable, then start considering purchasing a Eurorack system.
Don't be over eager. Learn first.