hello, i personally think that learning chinese has better advantage. once u have learnt it, u can go to many places like malaysia, singapore or any other countries that speak mandarin. In addition, i heard that mandarin is very much similar to japanese, so u should have no problem learning japanese too after mandarin..

As for your other question, you should start up with white belt (beginner) level and watch the videos in there.

Good luck and have fun in learning mandarin :D