I play a 4-2-3-1, I've not been able to sign too many player but those I have are pretty world class and formation puts everyone of Arsenal's key players in their best positions, the only downside is that there's no room for Eduardo and Van Persie in the same team, although I've been training RVP to play in AMC.
The signings I've made I would recommend:
Toulalan, 16m in the 1st transfer window (although I'm sure those of you who are more canny could get that price down)
Van der Vaart, a bargain at 8.5m as far as I'm concerned (1st window)
Enke, free transfer at the end of the 1st season, quality keeper, RIP
Gourcuff, 20m, world class attacking midfielder, spent a lot of time unsettling him as Bordeaux don't want to let him go
Mertesacker, 17.5m, expensive but worth it I think because IMO neither Vermaelen nor Senderos are quite up to scratch as 1st choice DCs (in the game that is). Mertesacker has great ariel presence and complements Gallas well.
(N.b. in order to spend 37.5 million in the second transfer window I had to have something of a fire sale, the likes of Gibbs, Bendtner, Rosicky, Vela, Merida and Djourou were all sold to facilitate these transfers).
My first team looks like this:
Goalkeeper: ---------------Enke
Defence(l-r): Clichy Mertesacker Gallas Sagna
Centre-Mid:---------Fabregas Toulalan
AMC: ---------Nasri/VDV Arshavin Gourcuff
SC: ----------------------Van Persie
Instructions are pretty predictable; RVP complete forward, Toulalan ballwinning MC(def), Arshavin Trequartista, Nasri+Gourcuff Attacking Midfield (One support, one attack).
The whole thing is working well enough, after finishing 2nd to runaway leaders Man City in the first season I'm top after 10 games of this. I also won the FA and League cup in my first season but was knocked out in QFs of Champion's League by Barca.