Most places in Iceland book out 9-12 months in advance. So while you are already late to the game for that, it can be done. You just may not get your first choices.
I personally do not care for RS maps or his book/videos for Iceland, sorry. I use the Lonely Planet Ring Road Trip book and have for 8 of our 9 visits. I also really like Iceland With A View, which is a website and she has a great You Tube channel. Her information has always been spot on for us. As for maps, I use one that I have had since our 2nd trip and it is great. It is huge though, but waterproof and tear proof. I bought it on Amazon for around $12 or so. I can write on it in pencil and then erase as well.
In 2024, a friend and I went sort of on a whim and did not book until the end of March for a late September trip. We did have to finagle the itinerary as places were already booked, but we made it work, to give you an idea. So don't give up yet!
This summer we too are avoiding the eclipse and looking at late August. I can't book yet due to my friends circumstances, so we know it may not be ideal, but oh well;). July is much busier than later August, and the later in August you go you might see the aurora. We saw it this past summer in mid August on the flight over.
We almost always use booking.com for places outside of Reykjavik. I will find places that way and then look at booking directly and compare. Note that many places in Iceland are very small and they don't have their own booking platform and use booking.com for it. Inside Reykjavik, I almost always book directly as our preferred hotels have a good offer for booking direct (Center Hotels, many locations in town).
Now if you are up for a camper van experience, IMO that is a really fun way to go and it gives you complete flexibility. The prices of those have risen considerable the last 2-3 years, but it has its advantages. We have used Happy Campers and were very pleased.
As for cars, we have always used Blue Car Rental, and 5 of those times were great but the 5th one was horrible and I swore I would never use them again. I gave them one more shot and it was good, but it was from their Reykjavik location which IME of renting there 3 times is significantly better in terms of vehicles and customer service. YMMV. Whatever you choose, we always opt for full insurance as Iceland has a lot of unique weather that affects cars and we just don't want to deal with any issues. For instance, in the strong wind, it is not uncommon for car doors to fly off, backwards, if not held onto. So even if you are careful, the car parked next to you may not be. Yes the full insurance is costly, but can be worth it. We normally use the Amex Platinum rental insurance, but for the possible damages here if anything were to happen we do not want to have to pay upfront and worry about getting reimbursed later.
