Thanks Ronin1973, all that information has been super useful!
So far I've been able to sync my synth with Reaper. In fact it was easier than I expecte, both the Minibrute 2s and the Drumbrute Impact have USB port and all I had to do is select the device in the Reaper settings and send clock signal out from the DAW.
I've also been experimenting with recording my songs in multiple tracks, one track at a time as I don't have any audio interface yet, but it has allowed me to test things out and make sure I understand why I need the audio interface and what I need it to do.
I also have more doubts and questions though, how do you guys do the multi-track recording? do you group multiple instruments in one track or do you strictly use one track per instrument? I find myself easily mixing more than 5 tracks at a time, would I need to get an audio interface with that many inputs? or should I be doing overdubbing with the DAW?
In my mind I would be doing everything with the modular synth and once ready, I would use the DAW for recording all at once in multiple tracks, so I can do the final equalisation in the computer. But I'm not sure that's doable with an audio interface that only has a couple of inputs.
I'm also facing an issue I forgot to mention in the original post. It is about the volume of my recordings, when I listen any of them, all sound way lower than any other audio so on my phone I would need to go full volume to listen it properly. I'm already 'normalizing' the audio in Audacity, I'd expect it to bring the sound to the max volume, but it doesn't seem to work that way, what am I missing?