In a rather complicated itinerary, we will have 3 nights in Rome at the end of a trip that includes a few days in Istanbul and a Greek Island cruise followed by a 2 nights in Athens.
Those three nights begin August 16th.
My concern is that I will find much closed on the Monday after Ferragosto - more so than a usual Monday in August.
What about the following 2 days?
Anyone with experience at this time in Rome would be much appreciated.

The Vatican Museums will be open on Monday (you can book on the Vatican website) along with the Colosseum/Forum/Palantine (although it might be too hot for those). For your three days, you might want to get the Roma Pass for 25€. It doesn't include the Vatican, but gives you free admission to your first two sites and discounts after that for other sites plus a 3 day transport pass. The Colosseum/Forum/Palantine count as one entrance.
http://www.romapass.it/p.aspx?l=en&tid=2

For opening hours I like to use Pierreci's website. You can search the sites/museums and the hours are listed.
http://www.pierreci.it/en/museums-and-monuments.aspx

Thanks for your reply.
How dire will the situation be for restaurants and shopping (and I'm not interested in the Nike store, lol)?
A large part of the pleasure in traveling, for us, is really good food (that doesn't mean five star but "chowish" and finding unique things.

True, half of Rome will be closed - but not the sights (perhaps some of the rarely visited, yes, but definitely not the majority of them). Just if you're planning on visiting some of those on-appointment sights (with one of the three soprintendenze), you might experience difficulty. Anything else, never mind whether overcrowded or less-known, will be open.
By the way, since you're coming from Istanbul... it would make for a terrific comparison if you visited the exciting ancient city walls in both cities - both capital cities of the ancient Roman Empire, as you will certainly be aware. Those walls, in both cities, are among the very best sights, rarely visited (particularly in Istanbul), and completely independent of opening hours and holidays, of course (open air & free access).

Ah, as a slow typer, I was cross-posting with you. Restaurants, that's certainly tougher than sights. You should check ahead with every place you want to dine at - you cannot count on them being open around ferragosto!

Much of Rome will be closed, but not necessarily the restaurants in high tourist areas. Sorry, that's what you may face.

Keep in mind that fine hotels with full service restaurants will generally have open (but possibly limited) service hours for that date.

Thanks for your replies.
We had hoped it might be easier to reverse our dates a little and be in Rome the very beginning of August (next week!) but United isn't cooperating.
Ah well, the hard earned tickets are "free"!