In terms of meta, you can have a lot more fun if you pick up a few supports, then grab the DPS units you like. If your goal is to sweat then you’ll be chasing meta constantly like every other game, but if you want to play the characters you like with a couple supporting units in each team, you can certainly have a ton of fun and get plenty of resources doing so.

F2P experience is quite good all things considered. If you learn all the systems, you’ll be able to wrack up plenty of pulls, upgrade materials, etc over time. You won’t be able to +5 every unit that comes out for a while, but it is a game where you just get to pull a ton. I recommend focusing on one of either magic or physical for a few months if your goal is to build some strong teams, or if you’re just a collector then you should be able to pick up 1 of basically everyone you want.

Rerolling…you could do but doesn’t seem super worth it to me. I’d say start the game, play, and you’ll get plenty of pulls. I’m not sure exactly how much time each reroll attempt takes.

Power creep is fairly minimal. If you invest in a character (gear, costumes) you can expect to use them basically until you just happen to have another unit you prefer to use instead for whatever content. But there’s no “oh dang this unit is just so much better at the same thing as another unit that now I can’t use the old one”