Hotel Bohinj Eco isn't actually at Bohinj, but at the nearest town. The lake itself is a few km away. The town is handy as it's on the bus route between Bohinj and Bled, but I don't think there's anything of note there.
I'd stay at the lake - we stayed at Hotel Bohinj, and it was lovely. Right on the lake for walking, boats/paddleboards etc. Or you can just relax on the 'beachy' area on the lake shore. We spent 3 nights there, which was a good amount of time.
The buses in Slovenia are excellent. We went from Bohinj to Bled by bus, then from Bled to Ljubliana and then Ljubliana down to Piran. All very efficient, easy to use and cheap. They're like National Express buses, in that you put your luggage underneath and they just go from town centre to town centre (so not lots of tiny stops on the outskirts).
I would stay in the different places you're interested in, rather than doing lots of day trips. They're all quite close together, but it's nice to be overnight in all of them.
Bohinj and Bled are quite different - the former is beautiful with the mountains right on the shore (and you can go up the Vogel cable car to get up into the mountains), and very relaxed. Bled is also beautiful, but is more touristy - not in a bad way, but it's much busier! Rowing to the island is fun though, and the lido was a nice place to chill for an afternoon. The castle is good too.
We stayed at a lovely place called the Old Parish House, and would highly recommend. Very central, but tucked away, and much nicer (IMO) than the huge hotels on the lake shore (it's slightly set back from the lake, but only by one flight of stairs!).
Ljubliana also well worth staying over. It's a lovely city - we stayed at B&B Slamic, and would recommend that too - definitely more of a hotel than a B&B, in a great location and really nice rooms.
Zell am See is a pretty town, and the scenery is lovely, but (IMO) not a patch on Bohinj/Bled. I've done it in summer and winter, and enjoyed it both times, but if I was offered the chance to go back to there or Slovenia it would be Slovenia every time.