I think you are on the right tracks and don't believe we have the cash to even think about adding Villa (or similar) at this moment in time, i.e. we are not at that stage yet were we can afford to make just the 1 big signing as opposed to where we are now where we probably need to make 3 (although we are getting closer).
So a summer of Johnson, one of Silva / Robben (even Simao although not as good as the other 2), and then a good quality with potential back up striker (like Kerrison maybe) would be good business for us.
Selling the likes of Degen, Dossena, Voronin, Itandje, Plessis, possibly Arbeloa (only if he really wants to go back to Spain) and Babel, and holding the others (including Masch & Alonso). Realistic and withing the realms of what we'd normally spend.