hey hey mtan
where are you arriving from and only 2 people? your first day will probably be jetlagged and "fuzzy". counting your days is really only 7 (dec 21 is arrival, time for passport/immigration, transportation to hotel, your departure day Dec 30 is checking out, getting transportation to airport? 3 hours for check in procedures)
your time is short, i would stay in rome and if possible for a day trip. i don't understand what you mean by "very/slow days dec 24, 25, 26, 28". rome will be very busy & crowded, many places may be closed, crowds doing the same thing you are trying to do, finding places to eat, if open check their days/times open. many close daytime (2-6pm), check if reservations available.
we stayed in the piazza navona area and near termini, wherever there were rooms available in hotels. we all have are own thoughts of where to stay, you will be walking a lot (wear comfy shoes/dress warm).
if you plan to take a cab make sure you go to taxi stop not hailing one on the street.
mercatocentrale.com
a big marketplace with restaurants, shops, bars, deli. roam around so much to see. don't know if opened christmas, many places don't have their calendar times up. keep an eye opened for them.
eatingeurope.com/ rome
eatwith.com/ rome
put your dates, # of people, click headers for lunch/dinner. residents cook in their home and you're invited. click the dates on calendar to see who is available for your dates. at least you know you'll have a holiday meal. good luck enjoy
aloha