i think it will be better to play 2 league games on a week. A 18 weeks season is too long and for a lot of people could be boring. Is it hard to change the structure of the league games?

no. the training should be the same... but the season must be shorter.

Or maybe only 8 teams in a division, instead of 10?
This way, the season will be 4 weeks shorter.

for example, i am very dissapointed that i am in 3.9 division... it'll get (18 weeks + break between season)x 2 to get to first division... and this if i am lucky and good manager.

IMHO it would be a bad decision to add even more weekly matches. The current planned pace with one league game, regional cup game and scrimmage game is already very big. A league match should look like an important weekly event for the team, and not just another game.