Will the iPhone 7 Plus fit in the OSMO Mobile with the case on?  I would hate to have the to take the case off and put it back on every time I use it.

It's possible but very tight and it adds weight.

A very tight case, yes.  A bulky and hardcore case, probably not.

ít fits in but the Problem is, when the case is also around the charging Point, you get an error message cause the Signal gets disturbed.

I bought the thinner case, can insert and remove easily, but you needs to adds weight to balance it.

You can try ESEEKGO iPhone 7 Plus case, it really beautiful and high quality. You can buy it on amazon.