Depending upon where you are, you might find a cheap flight.
If you don’t want to travel with your own bike then consider renting – http://www.tickettoridehighlands.co.uk can sort you out if you book early enough.
It starts early and you need to consider what clothes you’re going to be happy standing around in for up to an hour in temps of 5 or 6 degrees.
The only “big” climb is the one out of Fort Augustus. Remember that it comes in two segments and if you can’t hear the piper, then you’re not near the top (the descent is awesome though).
You’d think closed roads would feel safer but there’s all sorts of cycling shenanigans going on. Keep your eyes open.
Most folk forget that it’s closed roads. Don’t be afraid to zip past folk on right-hand bends when they’re all sticking to the left. FWIW I reckon that going the wrong way around the Drumnadrochit roundabout is slightly shorter/faster.
Although the start should see the fastest folk off in the first groups, there will be some slower cyclists in there too – the ones afraid of missing the cut-off time.
The road surfaces are generally pretty good. Standard road tyres will be fine (for me that means 28mm).
Water/food/service stops are pretty well organised.