Winning LAGs play very good postflop. When you only play premium hands, postflop decisions are generally not too difficult, with exceptions obviously. Playing the non-premium hands can put you in difficult situations much more frequently.

It has been my personal experience being a LAG that you shouldn't play too many tables at once. I do 2 or 3, 4 can be doable. You need to observe your tables and figure out who are the calling stations and who can be run over. I'd recommend just playing 1 table at a time until you get comfortable with your new style.