Hi Quarto,
Flew up there 2 Jan's ago... didn't stop at Fair Isle. We took a raft and were pretty dressed including life jackets (flew a PA28) just because of that time of the year but didn't wear suits. If you want to hire all that type of equipment and possibly save yourself the weight taking it there...then I'd strongly advise you give Andrew Bruce (FBO at Wick a call) he rents out equipment for transatlantic flights. As far as I know there still isn't a handling charge in addition to the landing fee at either Wick or Sumburgh.
Have a great flight!
EG