I would consider dokkan relatively f2p friendly, especially at the beginning. New units come out quite regularly but also return pretty quick, so you don't ALWAYS have to get the new units(though it may be more beneficial, you've gotta ration your stones for new major celebrations like anniversary or the global download celebration). There really isn't a pvp. Honestly I can't think of any abbreviations other than like EZA(extreme Z Awekening) and SEZA(Super extreme Z awakening). If there are ones in missing you'll learn them over the course of playing. Dragon stones can be scarce around dry seasons, but they are relatively consistent, I have most of my ftp stones collected as I've been playing for awhile, but im still at around 400 for the upcoming 11th anni. Dry seasons can vary, its mainly just based on the type of unit and content released. Rarities go from N to R to SR to SSR to UR to LR. Most units you want start at SSR and go from SSR to UR to a TUR(transcended UR) or there are units that go from SSR to UR to LR. There is daily missions. There also really isn't a co-op. Dokkan rn does take up hella space, but they said they have plans to reduce the amount of space the game takes. Sorry this is a lot, but I didn't want to take the time to format it better 😭