Is it advisable for me not to play more than one tournament online at the same time? What do you think?
If you are a new player and do not have a refined standard strategy in place then you should play less tables. I would suggest only playing 2 tables max if you are not accustomed to playing multiple tables. It is definitely advantageous to play in less table because you will end up getting info on your opponents when you spend a lot of time watching their style of play.
Just do what thinks works best for you.