Heyho!
I also met my boyfriend via internet and until now we met 3 times (1 time in Japan for 1 month and 2 times in Germany).
I can only tell from my own experience, that it might be a little hard sometimes to be with a Japanese guy because a lot of them really have problems in expressing their feelings. Sometimes I really want lovey-dovey stuff, but he has troubles changing into 'flirt mode'. So it is possible that there will be times when she really is feeling a (cultural) difference.
On the other hand...
I have a friend and her bf is also Japanese. He is quite different. Very lovey-dovey (kinda feminine, though).

About long-distance relationships: Not impossible. Very hard, the good-bye is always painfull (when i left Japan, I was crying like a baby...).
But there are positive side effects. I became very good at university and I never have troubles with my schedule (no dates that take much of my time).

In the end, it is all a question about character and personality. And you can never know what will happen. ;-)