Rather than go on about how great Iceland is (it is), I started making a few notes about what I learnt from my last trip. What I'd do again, or avoid. It's only based on limited experience, but the written guides I found online generally try to be comprehensive and that quickly gets overwhelming when you're just trying to plan for a few days. So these are my opinions as a solo photographer, in a van, for a few days.
1. Forget about the Golden Circle. I guess that's easier to say having already explored it, so it might feel like you're visiting Paris and avoiding the Eiffel Tower. It's great for proximity to the airport and Reykjavik but for photography you can find better, more spectacular, less visited sites to photograph elsewhere.
2. Head to the south coast. I heard from a local that the north east can be a great option too, so maybe I'll try that next time.
3. Stay near Vík (for the plane wreck and beach) or Höfn (for the ice lagoon and glaciers), or both, or get a camper. I hired a small camper van for my trip and it worked really well, once I'd figured out all it's features and organized my stuff.
4. Prioritize trips to the plane wreck at Sólheimasandur and the Jökulsárlón Glacier Lagoon. Both are popular, but with a little planning you can escape the crowds (at least in October). I enjoyed Reykjavik too with some quirky little streets for some street photography and the impressive Harpa concert hall (reflections everywhere), but I wouldn't say it's a must.
I loved visiting the plane wreck. There's a car park on route 1 but no sign posts other than an info point in the car park. You can find it easily on Google Maps though. It's then about a 2.5 mile walk to the wreck. When I got there I was first to the wreck, maybe 20 minutes or so before sunrise but another couple arrived soon after me. Going back I'd plan to be there very early and photograph through the blue hour. It's not necessarily a problem to have a few other people there but guaranteed there's soon someone wanting to climb onto the wreck for a prolonged selfie session with arms held aloft.
Follow Google Maps directions and you'll have two choices of car park on either side of the bridge where the water from the lagoon flows into the ocean. The car park by the lagoon (on the inland side of route 1) offers more options since it's an easy walk to the ocean beach from there too, but I used both anyway. Viewing the lagoon from here was fairly crowded but walk a little way along the beach and it's easy to get away from everyone. I preferred the west side of the bridge. For the lagoon, there are two other parking lots to the east along route 1 that give great access but with far less people and very different views. Well worth doing. Also park at Fjallsárlón (signposted for Iceberg Boat Tours) - ignore the tours and take a short walk for closer view of the glacier.
I got pretty much the cheapest I could find, through Camper Rental Iceland, and it worked out well as long as you don't mind diesel and a manual gearbox. It came with cooking gear as well as a decent sleeping bag and blanket. The little features I appreciated most were being able to step from the drivers seat into the back, and the little heater. The heater ran from a separate battery, along with two additional usb sockets, so could be left on all night. The heater was excellent, I had it set at about one third power and that was fine for the October temperatures, which were just touching zero celsius at night. Campsites were typically $15-20, but it's easy to find a spot to park elsewhere too (there are a few signposts in car parks that overnight camping isn't allowed, but I didn't see many). Swimming pools are the other best option for showers. Many parking spots along the ring road have toilets.
Rough Costs for 3 days (in US dollars) Camper van - $250 Fuel - $112 Campsites/parking/showers - $48 Food - $25 (I took plenty of snack food with me from the UK, and lived mainly on fruit, nuts and chocolate. Restaurant, cafe food and alcohol is very expensive. Supermarkets and gas station food is much cheaper.)
Stuff to take
I didn't take much, but the few key items that helped significantly were a towel (I took a light 'travel' towel and that was fine), headtorch and some thermal underwear. I didn't miss much, but a power bank for phone/camera recharging would have been great (mine broke on the trip before I even reached Iceland). In terms of camera, I shot on the Fujifilm X-T3 with the 35mm f/2 lens. I wider lens would sometimes have been nice, but I used my phone, a Google Pixel, a fair amount too. I also downloaded a map of the whole area into Google Maps, but I often had good LTE reception and data on my UK sim card anyway.
Next time I'd love to have the time to do the full loop of the island, but that needs probably more time than I'm likely to devote to it in the near future. I did give a ride to a french couple, hitchhiking and camping rough around the island over 3 weeks. If it's just me, I would take a camper again but I would ideally like a 4x4 to feel more free to explore the sideroads that are usually unpaved, but that pushes up the cost. And I think would head north. Around the coast again but in the opposite direction. Plan a few main stops but otherwise take a few diversions and see what comes.
I'm still working on the images I took but I'll hopefully have a little sequence put together soon.