a lot of things can go wrong in a planted tank and i mean a LOOOOT
these will basically cover the basics of a planted tank
1) what do you have under your hood ? (lighting)
2) what do you have under the plants ? (substrate)
3) what fish do you have ?
4) what plants did you use ?
and regarding your second question, YES
some people even grow some aquatic/terrestial plants emmersed for easier farming