It only becomes a problem when he prefers to do that than make love to you! Other than that, no physical problems, just that it can take over and then it would become a problem. I would say it is a little excessive though to be honest.
Aye why not. The only problem would be if you were there and didn't help him. Do you just stand back and watch him or count the tissues to see how many he had?
Perfectly normal, if he enjoys it why not? We all get the urge when our respective partners are not around. But even if i were around I would watch lol! Yum.