1 It’s never too early. Also I personally suggest you give KameSame a shot over KaniWani.
2 Don’t worry about it. No seriously, one of the main benefits of SRS is that it removes the need to actively plan your memorization study. Burn reviews are after a 4 month interval anyway so it’s really not important. As long as you don’t check your upcoming reviews and study all the items right before a review you’ll be fine.
2.5 After the earliest stages you need to expose yourself to the language anyway, with more exposure always being better. It’s not like avoiding Japanese is going to help you learn Japanese through the sheer unbridled will of the Crabigator. ᕦ(ò_óˇ)ᕤ