Stac Pollaidh One of the Assynt Hills
Hey Micha. Well, it is the most difficult question and I fear I don't have the answer. Scotland is Scotland, you never know how it will be. But generally, people say the best time to visit Scotland is mid April (but you have to be ready for some snow and low temperatures) and May. This year May was very wet and wasn't as good as it was expected. September was really good this year, but when I was in Scotland in September 2012, it was very wet. The best thing is to check the forecast and go to the place where it is supposed to be good. That's what I do. I hope you will have a great time in Scotland. Cheers.
Stac Pollaidh One of the Assynt Hills
I usually camp. There is a lot of campsites in this area (Ardmair for example) and you can also wild camp anywhere you want. I usually stay in B&B in Ullapool since it is only a couple of minutes by car to get to Assynt. There is also a youth hostel in Lochinver. But camping in remote spots is what I would recommend. But it depends on what do you prefer. Cheers.
I have to add more information about the time to visit Scotland. From June to September, there is a lot of midges who can be very annoying and can ruin your stay in the campsites. It is also the thing you have to count with.
Climbing the Zittergrat in Engelberg
Looks great!