I've just got back from Mull on Saturday. My species count included : Great Northern Diver, Golden Eagles, Sea Eagles, Little Grebes, Dippers, Kingfisher, 2 juvenile Brent Geese, Buzzards, Ravens, Hen Harriers, Kestrels, Sparrowhawk, Red Breasted Mergansers, Otters, Common Seals, Red Deer, Mountain Hares, Speckled Wood Butterfly.
You may wish to book an organised wildlife watching tour (I did mine with David Woodhouse and this helped me to find both Eagles, the Kingfisher, the Otter and the Diver which I wouldn't have located otherwise). However I know most birders (me included ) prefer to find their own as it is far more pleasurable to do it this way. However as I don't drive my options are limited and organised tours are the only alternative.
I think you ought to go and enjoy it !