If you do well in 4.0 leagues, you'll do fine in 4.0 tournaments. The skill levels of the players won't be that different. I don't think 4.0 tournament players play 4-5 times a week any more than 4.0 league players do.
The major differences will be that you will be playing singles rather than doubles, and you'll have to be fit enough to probably play more than one match per day. Only you know if you can overcome the differences between leagues and tournaments.