Which version should a beginner use, online or desktop?
Either; they read the same project. Beginners on managed or borrowed machines start faster in the browser because there is nothing to install or update. The online vs desktop page compares the two in detail.
Is Resolve too hard for beginners?
Only if you start with the whole cockpit. Import, trim, title and export is reachable in the first session; colour, Fusion and Fairlight wait until a project actually needs them.
What computer does a beginner need?
A machine that runs Chrome with a stable connection handles the browser studio. Heavier footage is proxied, so an older laptop stays usable.
How long until a first paid edit?
That depends on the work, not the tool. The fastest path is repetition: one small project a week, exported, watched, improved with a single new skill each time.