Please help us with Italy Itinerary...include Slovenia?

I love Slovenia and would highly recommend it. Given that everywhere else you'll visit will be overrun with tourists, Ljubljana might be a nice vacation from your vacation! (Actually, Ljubljana now gets its share of tourists, just not at the level Italy does.) Lake Bled is pretty touristy, though.

However, your Italy itinerary (which we can't see in detail) already looks pretty rushed? Are you just trying to pack in as many things as you can possibly see in the short time you have?

I'm with Andrew -- what you've packed into your trip so far leaves me exhausted! But to your question: if I had to pick one on your decision list I'd go for Ljubliana.

Another vote for Ljubljana!! Our newest favorite city. Charming, pedestrian friendly, less touristy, incredible cuisine, all around great vibe. We enjoyed 3 weeks starting in Venice, then joining the RS Best of the Adriatic that included Slovenia & Croatia. September weather is a plus.

Before you start making plans to extend your trip beyond it's original list of places (which is a long list), do a reality check on yourself. Stop talking in vague generalities (which allow you to willfully delude yourself), get specific about dates, including flight arrival and departure times. Do this now, before you list grows. Why? Because, frankly, Most People Cheat. When you wave around squishy dreams like "17 or 18 days" it's easy, tempting, and common to tell yourself little white lies about how much time you really have.

Make your plans based on actual dates (either booked, or proposed), not hopes. What date (and what time) will you arrive. and what date will you leave? Until you get that specific, you can easily lie to yourself, and many, many first-time travelers here do exactly that. They start off saying they have a "two week trip" and it turns out they have just 9 or 10 full, usable days in Europe (because they're counting the time from when they lock the front door at home and head for the airport, until the time they get home, or worse, they are just thinking about how long they're taking off from work). You need to account for the time it takes to get there (and home), so start with proposed dates for arrival in Europe and departure for home (and don't count your arrival day, no mater what time the flight is scheduled).

Then, take a hard look at your "must do" itinerary for Italy and see if that really leaves you an extra 3-4 days, or if (as is so often the case here with first-time travelers) they actually have too much moving around planned and not enough time actually being there.

IF you really do have days to burn....personally, I'd probably spend them in Italy (either allocating more time to your original itinerary) or just add a bit more. All the other options you're considering are lovely, but they all deserve more than "3-4 more days" (which i suspect may turn out to be less than 4 days, too ;) ).

We probably won't make it back to this region for a very long time,

Only if that's your choice...I'd urge you to set that kind of thinking aside. Maybe you'll like Europe enough to find a way to get back sooner than you think (something that many people seem to change their mind about).

Good luck, hope that helps.

Excellent advice from David.

Thank you all for the suggestions and advice, we are both really appreciative.
David - Thank you for the post. You are correct, we will need to factor our time traveled. Taking that into account, we're looking at roughly 16 days after factoring in travel.

Below is our rough itinerary, we'll know more as we start to book lodging and so forth. We're currently planning on using all public transportation. From all of your responses, it sounds like Ljubljana would make an excellent stop, however, we'll have to weigh that against adding an extra night or two to an already packed Italy itinerary.

Fly into Rome
Naples (Pompeii, Amalfi coast) 2 nights
Rome: (Historical sites, Vatican, Museums) 4 nights
Florence (Tuscany, Cinque Terre, Pisa) 3 nights
Venice (Lake Garda, Venice Lido) 3 nights
Dolomites Mtn range: Stay in Val Gardena or Alta Badia 2 nights
Total of 14 nights.
Fly out of Venice

I’ll chime in at this point to say that, in my opinion, you are still being unrealistic. The rule of thumb often invoked here is 2 nights = 1 full day after packing up, checking out, getting to rr station, airport, or car rental office, travel, and checking in to new lodging. 1.5 days max. Example: 2 nights for Naples, Pompeii, and Amalfi Coast? Pompeii alone warrants at least half a day. If you go there, you really should visit the Nat’l Archaeological Museum in Naples. Most of the artifacts from Pompeii are housed there. Even if you don’t stay a night on the AC, you need a full day for exploring some of the towns.
3 nights for Florence, Tuscany, and the Cinque Terre? Madness! Tuscany is a very large region with many lovely and varied towns. Florence is a treasure trove of history and art.
In my opinion, the CT don’t rank as must sees for a first trip to Italy, despite all the hype promoted by Rick Steves and others. If you go to the Amalfi Coast, you will see similar, but better scenery, along with other points of interest.
On the general issue of how long it might be before you can return to the region . . . You are young. There are several threads here that you can access addressing how non-affluent people afford to travel. You will have a much better experience if you let go of the idea that you need to cram in as much as possible and think instead, we will return.

After reading the practical advice, I would agree with the adage, "Less is more." You have certainly chosen some lovely locations.