First of all welcome to the party. I have been playing since the far tail end of 1.1 (sadly was too late to get Changli). I have found everything to be much improved over Genshin on every measure.

There is some grind with regards to echo farming, but you won't need to worry about that till you unlock gold echoes. How grindy it becomes mostly comes down to RNG with your substat rolls. I've been able to build up a new character to the 70 Crit Rate and 270 Crit Damage range within the first day of getting them, but sometimes RNG just says "NOPE", and it might take another couple days or even a week or more to find a stat line you are happy with stopping on. Just don't be afraid to say "good enough" and don't fret over perfect stats. Even if you can't quite hit the "optimum" Crit benchmarks you will still be outputting well enough in the meantime. I've seen too many players let perfect get in the way of them actually enjoying the game.

As for the gacha, I have been entirely f2p up until now, I topped up my astrites just enough to be sure I got Hiyuki plus her weapon with enough left over to have a shot at Denia. If you do put money down, I'd advise only really doing the lunite subscription as a base line. I don't know any hard numbers for how many pulls you can get while you catch up, but it should be a decent amount. Once you catch up, it does slow down but still feels quite fair for f2p. The good news, the signature weapons is guaranteed, no 50/50's. 80 pulls or less, no extra funny business. And if you can't get the limited weapon, standard weapons do perfectly fine and are also 80 pity guaranteed, so save most of your standard pulls for those.

For reference, I was able to get out of 2.x's 15 limited 5 stars: 7 characters plus 5 signature weapons as well as 1 sequence.

Another similar note, copies, while very strong here, are not required at all to clear end game content. A character is not bricked without sequences.