As far as destination suggestions go, your choices are fine but I would include a visit to Lake Bohinj. Three full days in Ljubljana are a bit generous, you could rearrange one of those days to Bohinj. The good thing about having a single base and doing day trips is that you don't have to decide on where to go until you're in Ljubljana.
We will spend the last Slovenia night in Kranj because the LB airport is only about 10 mins. away and we can easily catch our flight to Rome (FCO) and the following day, back home.
Kranj is indeed just 10 minutes away from the airport but Ljubljana is just 30 minutes away. Don't feel the need to stay close to the airport on your final night, it's tiny and easily accessible by taxi, bus or shuttle. That said, there are no direct flights from Ljubljana to anywhere in Italy. However, there are direct flights from Trieste Airport to FCO. If you were to decide to fly out of there instead, you could easily spend your last night in Trieste. Trieste is an easy 2-hour bus or train ride from Ljubljana.
I read that the villages in Slovenia pretty much close up around mid October for the winter and I'm wondering if we will have problems finding loding, restaudrants and transportation (buses between LB and day trips). Should I be concerned?
Perhaps you meant Croatia? I haven't heard of a village around here that will completely close up for winter, although some hotels in places like Bled and Portoroz do close down for maintenance for a couple of months between January and March, not in October. I wouldn't be concerned at all. Although there are buses that only run in the summer months, those would be an issue if you were planning on visiting more remote rural areas like the Soca Valley or the Logar Valley.
Am looking at airbnb.com for a little 1 bedroom apt. or studio in LB that would be w/in a ½ mile from the "attractions", train and bus stations.
That shouldn't be hard to find, anywhere you choose in the city centre will be fine really, you could even spread out your search into the leafier Prule and Trnovo neighbourhoods south of the centre.
PS: The commonly accepted two-letter abbreviation for Ljubljana is LJ, not LB. It features on Ljubljana-issued licence plates, too.