if you aim to champ D2 for SBBL, obviously you need time... like Eric said, at D3, income is very low if you brought your expensive players down the D3, ended up you don't have enough money to fund him. Unless you relegate to D3 bringing only those 4000-8000k players, then should be fine.
But if you are looking for challenge, to win games while grooming your draftees, D2 will be the right place for you.