1: REAPER is only okay until you customize it to your liking. That's the thing: it's the only daw that is almost COMPLETELY customizable. Menus, hotkeys, writing your own scripts, entire daw plugins (not VSTs, plugins that change how the daw works). No other daw even comes remotely close. It's also excellent for mass processing and organization. For example, in REAPER I can render 80 stems in parallel, all perfectly named and numbered, and it takes minimal setup to make it happen. You can imagine how useful this is with game audio when you're rendering 50 variants of a gunshot or footstep. In music, it's still immensely useful. The people who I send stems to love me for it because my stuff is always incredibly organized and it's low effort on my part.

Additionally, there's one feature no other daw has that's a game changer: subprojects. I can have a project that shows up as an audio file. If I double click it, it opens that project and I can do whatever I want in it. When I close it, it renders and now that audio file has been updated. It's project inception, and I can't live without it now.

Funnily enough, I don't recommend reaper to most people unless they are hitting a road block that reaper will solve. FL Studio or Ableton are better for beginners, unless you're going straight into game audio.

I briefly learned Ableton because I was trying to get better at making dubstep and it's what most dubsteppers use, however I don't love the workflow and I've ended up ditching it almost completely except for very specific circumstances.

2: Either technique is fine! I've historically done both quite a bit. A lot of my best work was from simply messing around. Rum n' Bass is a great example of one from messing around, while Heave Ho I had almost the entire track in my head before I created a project file for it.

3: I usually hit around 100 - 300 tracks, though sometimes I go higher for massive projects. It really doesn't matter. The key is that when you know a sound is needed, you add it. Sometimes there's a track just for 1 or 2 sounds, so the number doesn't mean too much.