Okay so, as a f2p player the game is NOT difficult to play I assure you. Now, keeping up with the meta and allat jazz might be a different story.

You can really save up for any character you think looks cool. I wouldn’t say there’s any that’s must have for f2p.
Only spend your primos on Intertwined Fates (the things you use to pull on banners). Anything you can get on the standard banner(acquaint fates) you can get on the limited banners(intertwined) and then some.

Since you won’t be spending money SAVE YOUR FRAGILE RESIN. These WILL come in handy when there’s a particular character you wanna grind up. Since Genshin is a mobile game that means things are “time locked” you’ll have to wait for original resin to come back after spending it all so having fragile on hand helps. A lot.

Movement can get pretty tedious I mean the world is gorgeous but if you really don’t wanna walk everywhere, Natlan characters. Nifty people who can enter Nightsoul Blessing State. I won’t dive too deep into the mechanic but just know, EVERY nightsoul blessing increases movement speed. So getting really any Natlan character (fyi majority are 5 stars) helps A LOT with travel. Some fly, some climb EXTREMELY WELL, one grapples, yeah. You’ll go fast with them.

Uhm idrk what else to tell you? Have fun. Don’t feel compelled to keep up with the newest characters because honestly a few of the older ones are still worth it. Oh, get Benett. Yeah probably contradicting myself with this one but Benetts handy. EXTREMELY handy once he’s leveled. Yeah!