Anons who have been to Iceland already get in here, pls. (Others too, of course - if you have an opinion)

So I'm planning to go to Iceland in a few weeks and I have a few questions:

What would be the best (and cheapest) way to get from Reykjavik Airport to Hornstrandir? Time is not really an issue, so I wouldn't mind walking some parts of the road (if that is at all possible). Otherwise does it make more sense to take a boat, a car or maybe a bus?

If you had the choice, would you go there in August or in September? What is the weather like? When does the "warm" period end in Iceland? October is a bad idea, isn't it?

Are there any dangerous animals you should be aware of when hiking solo with a tent?

Also, general recommendations of what to see/visit in Iceland? So far, I planned to go from Reykjavik to the utmost north (Hornstrandir) and back again. Also the area around Reykjavik (the golden circle).

Thanks in advance.