OT Contractor Question

The wife and I are contemplating getting out of the city to somewhere with more space and buying a home. One of the ideas we had was to buy a fixer upper (or even a foreclosure) on the cheap and renovate.

Obviously this involves construction, and with it all the hassle. A couple of questions:

1)How common is it to retain an architect for a house renovation like this? I work at an engineering firm, so I can do the MEP/S work, but I'd like some direction from an architect so my house doesn't look like an engineer designed it . Also, I know nothing about the residential side of things. Further, how common is it to retain them as a CM in addition to designer?

2)On the contracting side, is it common practice in residential construction for final payment to be made upon successful final completion of all punchlists rather than substantial completion? My fear is that by doing that some subs will get pissy and threaten a lien because of other subs holding up the works.

Thanks