Hi there
I fish the scottish Lochs regularly at this time of year but have not fished Voil.
It's difficult to say what flies or Lines will be best as the weather is still very changeable - I experienced fish taking flies off the top in a southerly wind 2 weeks ago, and 20 minutes later the wind had swung to the north and it was snowing! the fish were gone...
flies really depend on which flylines you are going to fish - Lines I would recommend would be a Floater, A clear intermediate and possibly a sinker like a wet cel 2 if you are fishing from a boat.
Again it also depends on what you are fishing for - I presume it's trout, although Voil has a lot of Salmon and the odd Char.
For Trout Flies, I would not go without Bibio's Kate McLaren's and a Peter Ross
You may also need something with a bit of weight if its cold. - Suggest black and Green
Hope this helps! Good Luck!