Well if you have your backwalkover its fine.. But make sure you stretch first... But if you don't have it then yes a spotters is needed.

If you have mastered the back walk-over, then no. It's just like any other tumbling skill.

if you can do a backwalker over then theres no need for a spotter

If you can't do it then yeah, obviously. But if you can do it by yourself then theres no reason you shouldn't be able to do it solo. Don't try it on a trampoline, it doesnt work. You can have anyone help you, all they need to do is support your back and help you kick your legs over, the rest is on you. You should be stretching your shoulders, watching your hands, and keeping the leg the kicks over first in line with the rest of your body. If you and your spotter have good chemistry and trust in eachother, then you should have it by yourself in no time.

if you have it and your coach says you have it then yeah go head