I have only 2 formations: 4-4-2 and 4-5-1, i think 4-3-3 is too OP in attacking and lack of middle field controlling, so i never use it, and the formations with 3 defenders are never one of my choices because for me success is "don't let them score"
But i will change formation if i meet some guys with stronger team than mine, i have the feeling that i would play against those guys in the next season.
About the transfer issue, i think i will wait a week before bidding for players, i hope that the aggressive bidders all got their players so they will leave the rest for me but it should be a huge disadvantage for me in the first days of season, i could be dropped behind in league and out of Cup competition. But it's ok, will cope with it!