I developed an Asymetric 4-5-1 that works well for my side in the belgian lower leageus. The false 9 (offset right)/ Shadow striker (offset left) combination works really well for me, especially as I have an Inside forward (support) on the right so my false 9 naturaly has 1 option either side of him and is in the right kind of area should the Winger (LM) look to put a cross in.
defensively I play 4 at the back, with 2 complete wingbacks, and a Halfback who is the key man as he can drop in centrally between the 2 CB's if both the LB and RB are up the pitch, if only one of them has pushed up then he'll move across to cover taht sdie more or if all 4 are back then he'll patrol anyone who comes at the back 4, normally working well against any CM that venture forward or CAM's, but he's also the man who picks up any full back's that push up the pitch when an attack comes in from out wide.
then I use a box to box mid to link the play between the attack and defence, I've recently picked up 1 that likes to play higher up teh pitch so he adds to the attacking threat by breaking through and trying to lb the keeper every now and again. (love that ppm)
I only chose that formation due to what I had available. 2 ST, 1 RAM/ST, 1 RAM/CAM, 1 CAM, and 1 LM who couldn't play LAM going forward with 2 DM/CM who I quickly moved to bring in a great DM to cover that area, who is still first choice now I'm in teh Pro League.
But as a general set of rules I'd say build a tactic to fit what you've got then pick a philosophy that suits it and then look for bargains that could come in and either cover what you think will be a key position or multiple positions and only introduce them slowly. putting 1-2 straight into the team is fine, but if you've got 4-5 new players to put straight into your team it won't work out very well as I've found it takes alot longer for them to gel that way then if you introduce 1-2 then slowly rotate the others in over the first 5-10 games. e.g. using them off the bench, then giving them the odd start until they seem to link up well with the rest of the first team.