That background mounting solution works well for a few months and then starts to peel. I used it on my 75g tank which I changed the background on, it took 2 people to get it on. Best if you use two people anyway, as it can get quite messy trying to put it on by yourself.
No harm in taping it on either, you can use scotch tape which wont show as much.
If you are going to paint the tank, it is best to do it without having anything in it and also outdoors. Allows you to move it easily and get a good covering of paint. I painted my 55g with Krylon Fusion Black spray paint. Krylon Fusion is known to be aquarium safe.