Mostly covered above.
Coast roads tend to stay clear of ice but there are enough inland and higher sections that it would be a consideration. The Bealach na Ba is closed at times.
100 mile days would probably mean some riding in the dark. Look at dynamo hubs.
Wild camping would give you flexibility but staying warm and dry for 4/5 nights might be a problem. Consider booking a night or two indoors. Of course, that would remove some of your flexibility.
Getting food might be an issue as many cafes etc (and there are few to start with) will be closed for the season.
On the upside, roads will be quieter and the scenery can be even more stunning (though you might miss some when night cycling)
Edit: I wouldn’t completely rule it out, just be aware of the added challenge and/or timescale