I believe your "definite" list is pretty much covering it all.
I went to Iceland last year and it was just absolutely brilliant. You can view my short impression
https://flic.kr/ps/2UBNJP Since it was a true holiday with the girlfriend I pretty much made holiday snapshots, so not much artistic stuff going. I really need to get back for some serious photographing! Below are some of my tips, you be the judge wether they're helpfull or not
Reykjavik is a great city, be sure to visit some local pubs for some great live music going on (music is a big thing in the city). The city itself is rather small, we stayed one evening + a full day which really was enough.
If you plan to go Whale watching I would definately advice to go to Dalvik instead of the way more popular Husavik. Dalvik has much less tourism, there is 1 whale watching operator who use 2 boats maximum. The boats are rather small and the crew is very friendly. On the trip back to the harbour you can go fishing. Back on land the crew puts your freshly caught fish on the grill. The boat is on one of the pictures. I would reccommend the 60-250 or possibly the 16-50 for the whale watching....these whales just were often waaaaay too close for my 135mm to really catch a good shot.
Myvatn is the most "active" part along the ring road with truly breathtaking scenery. However be aware that Myvatn is Icelandic for mosquito lake...and it lives up to it's name.
We visited the eastern town called "Borgafjördur Eystri" which is a small place with some great hiking trails nearby. It is a small bit "out of the way" so not much tourism going on. The road towards it was a bit tricky though (steep climb, big drop and 10 meters visibility due to fog). It has the best puffin rock that we visited.
Icelake...James Bond went there so you must too.
Golden Triangle.....very touristic. A let down after visiting the other parts of Iceland, just way too much tourism (90% of the people visiting Iceland never leave Reykjavik except for the "golden triangle" tour). The rest of the island isn't spoiled by tourism at all, which we loved.
Sometimes on the hot spots people can spoil that scenic view of the waterfall. Just wait a bit, we noticed that 99% of the time we were the only people staying for a bit longer and the rest of the people had to catch the bus again within 20 minutes to continue their "bustour"
One last thing, Iceland has very little wildlife. There are birds (puffins!) and a whole lot of sheep (crossing the road all the time) but other then that not much going on. The reindeer are import from scandinavia and we didn't see one. However we did have to run for our lives when we got attacked by a couple of "squa". They are a rather aggresive bird, comparable in size to a seagull...just a tad bigger. They're really nasty and made sweeping dive attacks on us. According to the guy we rented the place from, the birds are known for making (mostly fake) attacks to scare away people (they succeeded!), however a poor fella was in fact killed a year before after a attack by one of these birds...the guy really knew how to make us feel safe