If you want to go through the Scottish TMA at FL100 then (a) you must have a transponder (mandatory above 6000ft) and (b) you must expect radar vectors to get you round all the climbing/descending traffic out of/into Glasgow/Edinburgh/Prestwick. All in all I'd say this is an extremely risky venture if you're not IMC-rated because the chances of being fully VMC at FL100 are low whatever the time of year.
I'd suggest if you want to stay high for fuel economy reasons then the best bet is get yourself to Dean Cross then route direct Turnberry (max FL85, partly in Scottish TMA), then via FULMA (edge of Scottish TMA) and whatever route you fancy from there north to Stornoway.
Have a think about refuelling at Oban - great place, fuel cheaper than Stornoway!
NS