Hi - we did a similar sailing last year so can let you know about Stavanger and Olden.
Stavanger is very walkable, you are moored right next to the old town and can easily walk into the new town, see the cathedral etc etc. Other options there are boat trips (locally or all the way to Pulpit rock) and these are all accessible very near the ship - no prebooking required on my cruise.
Olden - we prebooked (locally) a coach trip to and from the Briksdal glacier and then walked up ourselves without using the troll cars. It was a fantastic excursion and much cheaper than the P&O excursion that did exactly the same. There isn't much to walk to in Olden - you have to bus out to places, other people were getting on small land trains for trips or going up to the cable car. Again right off the ship was a local agent selling all of the excursions independently. The did a lovely sailaway for us as well.
We were supposed to stop in Haugesund where I had booked a local excursion to a goat farm/homestead but we missed that port in the end. I got a full refund from the local operator.
Our other port was Hellesylt where we did a RIB trip out to into the Geiranger Fjord. This was both spectacular and exciting and I think you can do them from Stavanger as well.