Base yourself in a couple of centres and explore
Inverness is fine if you want to do the north west and across the top of Scotland.
Try to go as far north as you can. At this time of year, the further north you go, the less motorhomes and nutters on sports bikes.
This hostel is good if you can get a room to yourselves. There's secure parking for the bike in the multi story right next door.
I'd do around the top of Scotland via Ullapool, Cape Wrath, Tongue and Alltnahara on one day.
Second day, head for the central north west : Kinlochewe, Torridon, the Applecross Peninsula and maybe a jaunt over to Skye. Retuen via Fort Augustus and Loch Ness side.
A third day from Inverness could take you down to Braemar via the wee road I mention in the "wee gems" thread.
Based in Oban, you could do an
Island rover ferry trip around the isles over a couple or more days. Make sure you plan well and book ferries and accomodation ahead.
Oban is a bit of an OAP bus tours magnet but there's plenty of places to stay.
This B&B is very good but not cheap.
Make sure you book ahead. It's pretty busy in August.
As to routes, you can't really go wrong anywhere in Scotland but you might want to avaoid arteries like the A9.
Embra is very busy at this time of year so accomodation could be tricky. Easier if you come later after the Festival, in September say.
See the threads on "wee gems of roads" and "roads to avoid" for a few ideas.
Lots to think about. Get those maps out!