Hey and Welcome!
I would say no more than four, two would even be better. You would be amazed how crowded it can get. I have a 100cm x 100cm and four is a bit too much with everything else in there. I don't have a strain to recommend, way to many nice ones out there. Look over the seed banks, take your time, there is so much to see. Choose a few and see if anyone has anything to say about your choices!
Peace and happy growing!!
Oh, and try to take a moment and stop by the Introductions thread and say hello!!