2 weeks in Italy Nov 29- Dec 13, 2018

I'm not sure why you would want to eliminate Venice and Tuscany during your time period. Granted, the beach areas are probably not a lot of fun in chilly December weather, but other than that, Italy is Italy. Your idea of taking guided tours in Rome may be wise because -- as you say -- there is so much to see. But allow yourselves time to stroll around on your own too.

I encourage you to read the RS guide and/or other popular guidebooks and narrow down the things that especially interest you. Buying train tickets in advance can save you significant money, the downside being that you need to catch that specific train.

Since you're flying in and out of Rome, you might want to book your first 3 or 4 nights there, and then return for your last 2 nights or at least the 1 night before your departure. In between, you could visit Pompeii and Herculaneum for a 2-night stay, then head north to Venice and work your way back south after that. Personally I wouldn't bother with Naples, but YMMV.

"It is early December and from what I understand, that basically prevents travel to the coasts and Tuscany. I am also putting Venice in that category. Am I right to eliminate those?"

Early December doesn't "prevent" travel anywhere, but it does mean that beach towns and places that have a "season" (like the Cinque Terre) will be off-season, with many restaurants and hotels closed. It also means rural Tuscany will not be at its best - think brown rather than green.

Venice is a city; it doesn't close. The weather may not be what you want (I have no personal experience, but have read it can be cold and damp), and you may run into the aqua alta (high water, when low parts of the city flood), but the tourist crowds will be minimal. If I were going to Italy in early December, I'd want to take advantage of Venice without the hoards.

From Venice on your way to Rome, you can see places like Padua, Verona, Ravenna, Ferrara, Bologna, and Florence. As a detour from Bologna, there's Parma and Modena. South of Rome, Pompeii should again be good because of the minimal crowds, and there's also Herculaneum. Naples is a fascinating city, albeit a bit stressful for first timers to Italy.

You get the idea - there are lots of worthwhile places to see that won't "close" and will be great to see in any weather. Start reading and watching, and figure out your own must-sees. Raid your library to get as many travel books as you can. Note that Rick's Italy book is great, with lots of detail about the places he chooses to cover, but he omits a lot of places too, so be sure to look at other books as well. Rick's videos are here (scroll down to Italy): https://www.ricksteves.com/watch-read-listen/video/tv-show

Congratulations! Both for 50 years and for raising great kids!
Look at the videos and guidebooks, think about what interests you the most (art, architecture, churches, ancient history, Renaissance, fashion, food ... so many things to love in Italy!!) Don't try to see everything -- just be excited to see what you DO see.

Pompeii will be much more comfortable without the heat and crowds of summer.

We're in our mid-60's and have been to Italy in July, August, September, October, March, and April, but our absolute favorite time to go to Italy Is November and December. We've been to Rome, Venice, Naples, and Florence in December (for a week each) and thought the weather was great and the lack of crowds was superb.

Venice only seemed cold to us one day when it was very foggy. The Venetians and their dogs were bundled up in down, but we were fine with sweaters and sometimes thin long underwear. However, we are Minnesotans, so take that into account.

Everyone is correct in saying that your job (your pleasure) is to think about what YOU want to see and do. For instance, if you love ancient Roman art and architecture, just plan on Rome (and Ostia Antica), Naples (for the museum), and Pompeii. If you love medieval and Renaissance art and architecture, stay in Rome and Florence, with day trips to some Tuscan hill towns. If you can't stand the thought of missing the uniquely wonderful city of Venice, do Rome and Venice even though the travel time between them is the longest.

Subtract half a day or more from your two weeks for every time to move from one city to the next, and don't count your arrival or departure days in your two weeks either. This will help you focus.

Anyway, December is a fabulous time to go to Italy!