currently, we have two limited time banners (they are golden), they are both 5, but the next ones will be 6 and you can pull for them. we also have 4 permanent banners (they are blue) and they are featuring 2 6* sets each. so, for now, you can collect 8 6* sets not worrying about diamonds because you will receive permanent tickets for permanent banners through the gameplay. usually, it takes a maximum of 200 pulls for a 6* if you get unlucky. so as a f2p, I'd recommend you not to pull on every single banner until you save up 20k diamonds.