Isn't sly a very sleek and slender character? rocket racoon is kind of short and stubby I thought. As far as I know the Rocket Raccoon figure is only like 2 inchs tall isnt it?
I'm thinking your best bet would be getting Rocket Raccoon for Sly, and maybe using some of the Jazwares 3 inch line for the bases for the other ones. As far as Murray, you might have to sculpt him, as I don't really know any good Hippo-bases that are out right now. But I definitely think the Sonic one might be decent, with a ton of sanding and sculpting.
Also, a TMNT head for Bentley, for sure.