To be fair, I'm not a 4-2-3-1 guy, I almost hate it hahaha. But I move to 4-2-3-1 from 3-5-2 and it is just solid, even with simple and not fancy roles such DM or AM, no IWB, no IFB, etc as base. At first I use BWM on defend and Regista, but now I think double DMs on support gives me more, but it really depends on the players. As for AM, I try use AP on support and SS, but the best so far is just AM on support, maybe give him instruction like roaming or move into channels. Wingers are flexible, sometimes IW, W, even AP or WTM, depends on situation