Hi we drove the hebrides last summer in the camper from Ullapool to Lewis then all the way down and off Bara into Oban.
Lots and lots of cyclists on the island most going in the opposite direction, from south to north as this is usually the most favorable direction for a tail wing rather than a head wind. The small southern islands are quiet with a nice remote feel. There are lots of good camp sites, god places to eat but some can be quite far apart.
Balranald springs to mind as a good place to stop off. Small family run site with good facilities a drying room and huge beaches.
https://www.balranaldhebrideanholidays.com/travel.aspx
south Uist also had a nice site with a brand new very nice bunk house. it would be a great place to stop over for a night or 2.
https://kilbride-campsite.business.site/
I posted a review of our trip on a camper web site it is not really cycling specific but may throw up a few ideas.
https://www.autosleeper-ownersforum.com/t30575-outer-hebrides-form-north-to-south
if thats not view able i can send it to you…….