Where to go on 2 separate very short visits

I'm afraid I don't know much about where you can have encounters with folk customs in Slovenia, but for the other things, I think you could spend your pre-program time in Bled and your post-program time in Rovinj (which is actually in Croatia but only about 80 km from Piran). Another option is Kobarid and the Soca valley.

Slovenia has a lot of beautiful scenery. I suggest Rovinj because it is a charming village, and in Istria you can visit a host of other charming villages.

I don't know anything about how to get where you want to go by public transportation, so I don't know how feasible these suggestions are without a car. So I'll throw out another option that will be much more doable by train: Ljubljana. I think it is one of the most delightful, accessible capital cities in Europe: very walkable and filled with great architecture. It may not hit the things you're most interested in, but I don't think you'll be disappointed if it proves too challenging to get to some of the smaller towns and villages via bus or train.

Thanks -- I'll check these suggestions out.

I wouldn't recommend visiting Rovinj after a week in Piran, the two towns are quite similar. Bled/Bohinj and the Soca Valley are the most obvious choices given your interests, although regions such as the Vipava Valley or the Karst could fit the bill, too. Folk customs aren't really readily accessible, you would need to be in a certain area during a local festival, patron saint feast or some other event. You haven't mentioned when you'll be visiting, but some well-known upcoming folk events include the Cow's Ball in Bohinj in September, the Karst Wedding in Monrupino/Repen in the Karst region in late August, the grape harvest in Goriska Brda, the Vipava Valley, the Karst and the inland region around Piran, etc.

Agreed about the Piran/Rovinj similarity. I think I'll add Ljubljana and the Soca Valley. Appreciate the suggestions.