More commentary than you probably want on the Slovenia part...
You are biking Parenzana Trail? The path of the old Istrian narrow-gage railroad that has been removed? I was going to do that but got rained out. It's supposed to be great.
Agree with others that one cave visit is enough. Škocjan has more walking, is more natural, and is a UNESCO World Heritage site. Postojna Cave has a train, is more commercial, and is not a UNESCO World Heritage site. If you don't mind climbing a bunch of steps, turn left at the end of the Škocjan cave tour to walk out of the gorge instead of turning right to take the funicular out. You'll be rewarded with a nice waterfall just off the path.
Tolmin Gorge is great. I liked it better than Vintgar. Tolmin Gorge felt more like nature to me; Vintgar felt more like an attraction.
I traveled solo and spent a day doing a handful of valley walks/hikes in the Soča Valley (not mountaineering) with Vesna, a local guide who is really committed to giving her guests a great experience. I liked her a lot. Her website is slocally.com. We hiked at 3 or 4 spots, each one diverse relative to the other -- from along the Soča River near Bovec to an Alpine Meadow path near Tolmin that took us to a hand-operated contraption that took us across a river.
The Kobarid Historical Trail was also pleasant. I hired a guide from the WWI Museum at Kobarid to give me a tour of the museum (which was excellent) and then guide me on the trail.
Alternative to Tolmin for lodging... look up pictures of nearby Drežnica, which is up a narrow (but not overly scary) 2-lane road from Kobarid. Kranjc Tourist Farm is at Koseč, just above Drežnica. It was a great base. Good dinners. Great breakfast. They did laundry for me for 8 euro.
The Cicerone guide Walking the Julian Alps of Slovenia can give you lots of ideas for Vršic Pass hikes. I did the hike to Slemenova Špica, which offered nice views across Slovenia and Austria.
Kranjska Gora and Bled are both very touristy. Lake Bohinj is less so, especially at Ukanc at its far end. If it were me, I would go on to Bohinj on the 18th and use it as a base for 3 nights (I used Ukanc as a base for 5 days to explore the region). It's a little further drive and you'll back-track a little on your Bled day, but it is so much more peaceful. I highly recommend Vila Park B&B at Ukanc. Lovely, lovely owner (who did laundry for me without charge). Spotless rooms. Super peaceful location. Amazing breakfast.
Vintgar Gorge is nice but you can make it great by doing a loop walk instead of an out/back walk on the walkways. At the end of the walkways for the gorge, hang a right, ascend through the woods to the Church of St Katherine, go through a gait opposite the nearby pizza joint to follow a path through a mountain cow pasture with great views of the valley/villages down below and Bled Castle in the distance. The path descends back down to the parking lot. More details are in the Cicerone guide mentioned above.
From there, you could spend a little time in Bled if you didn't do so the previous day, followed by Radovljica (the latter was a pretty quick stop for me). Begunje is an alternative to Radovljica. Less medieval charm but more real village life. Things there include a cute church a the top a hill, the Museum of Hostages that is located in a former mansion used as a prison for resistance fighters and their sympathizers by the Nazis, a memorial to those executed by the Nazis, and castle ruins. Sašo at the TI office gives a great tour and is part of a group restoring the castle, so he has a key to get you into the castle's tower so that you can climb it to the top. He also has great stories about exploring the castle as a kid (and growing up in Begunje), and he can take you up a path in the forest to a mini-castle made during medieval times to house the devil/a demon.
