A few tips:
* when travelling through south Uist try and get off the main road. It heads up the centre of the island which means you don't see some of the more interesting parts, there are various small tracks/roads that will let you explore the west coast, try some of them.
* Don't rush up through the Uists, try and enjoy them, a lot of people ride the length of those islands in a day, I think they are missing out.
* Make sure you spend some time exploring Berneray, it is a real gem of a place, not just the place to catch the ferry to Harris.
* Harris is tricky, the west coast has fantastic beaches, the road on the east coast (the golden road), is a wonderful road to ride (though hilly), if you can try and do both, oh and then there is the ride out to Hushinis/Huisinis.
* Than camp site at Lickisto has some great pitches and a nice Blackhouse/common room you can use to escape the midges and meet others if you want some company!
* The Gatliff trust hostels are basic but can be great fun, they are all in fantastic locations and a way to escape the weather if you need it.
* It can be very, very windy on those islands, think about what tent you want to take, I spent the night on Barra wondering if my Terra Nova mountain tent was up to the job it was, but not everyone is so lucky!
* If the weather is good then the Hebrides is a fantastic place to cycle, if it is bad it can be really hard work (a few years ago I rescued a couple that had been blown into a ditch on Lewis, we managed to squeeze their bikes into our hired minibus). Some days it is best to just sit out the weather.
* Make the most of the CalMac ferries they can make the journey part of the adventure (and they are very cheap if you are on foot/with a bike)!
* Only go to these islands if you are prepared for the consequences. For some of us they get deep under the skin. If this happens to you, then you may find yourself heading north far more often then you expected and become an island bore (guilty as charged). You may even be tempted to go and live there (looking at you you tigger!).
In terms of a route, a couple of years back I returned from Harris via Skye, Mallaig, Moidart, Ardnamurchan, Mull and then back to Oban. I found this a really enjoyable route. You could easily wake up in the tent on Mull and be on the train home in the same day. See https://www.crazyguyonabike.com/doc/?o= ... 10600&v=90
for more detail then you probably want.
Have fun, I'd be envious except I'm off to North Uist in two weeks time (like I said it gets under your skin).