Why not land at Tingwall instead of Sumburgh? It's a hell of a lot closer to Lerwick - and no 'security' bull!!!! to go through to get to your aircraft. Avgas is usually available there (but check first). A lot cheaper by taxi to town ~10 mins vs 30-40 from Sumburgh.
Before landing at any of the strips I'd strongly recommend you talk to one of the pilots at Tingwall. There are some deadly serious wind limitations for the strips at Fair Isle & Foula, and local knowledge stuff for most of them.
The ph. number is (was?) 01595 840 246.
In summer the bird observatory on Fair Isle has accommodation. Foula has a B&B, Lerwick various B&Bs + hotels etc. Unst has an airstrip if you'd like to go further north as do Fetlar, Out Skerries, Papa Stour & Whalsay. Most islands have B&B accomm.
Be warned that most strips are short ~450-500m. Out Skerries is 380m with obstacles.