Interestingly enough, the guy who won your league last year promoted to my IV division. Despite being projected to finish in last place, he's managed really well despite a lack of player salary and will probably make the playoffs. That just goes to say that I think it's never a good idea to purposely not promote, as some have suggested.
As for what to look for in big men, I'd rate the important stats as ID/RB first and everything else secondary. Additionally, I'd go for an older guy, 28 at the youngest because you'll be in a crunch for money as you really need at least 3 new starters. Also, you'll be giving away money by not putting in a really big stadium upgrade if you do promote, so you simply can't afford to spend the extra money on a young or even medium aged player. Scrap by with decent old guys until you get your foot in the door. And study what Midwest Bulldogs has done this year because he's really been a model for overachieving.