North of the Central Belt...
... just about everywhere is worth going. Save the A9 for the way home, though.
Coming up from England, the A1 is a bit dull but OK, the M74 is just another motorway; I'd recommend the A7 from Carlisle-Edinburgh or going round via Dumfries and getting a ferry across the Clyde if you go up the west coast.
I did something similar last July, before the English school holidays started but after the Scottish schools had broken up. B&Bs were plentiful and mostly quite cheap -£25-30 a night - although some places may charge you for both beds if you're alone in a double room. I just went on spec and never ended up sleeping in a barn, although turning up on Mull on the last boat and only then finding that it was the day of Tobermory Highland Games made it a bit exciting. Camping is pretty easy and wild camping is, I think, legal (I didn't do it). Take it a bit steady on the single track roads, watch out for sheep (when I was there, the ewes had been shorn but their lambs hadn't - I quickly learnt to watch in particular for woolly sheep on one side of the road and clean shaven ones on the other - the lambs *will* cross the road to follow their mothers when they run away from you. I could not possibly condone going totally beserk on the totally deserted EU-funded wide and empty main roads that turn up here and there as well. If you are going island-hopping (and you should), then check the Calmac website for combination tickets - the ferries are a bit pricy, but you can save some by buying tickets for all the crossings on your route together if you're doing (eg) Oban-Mull, Mull-Ardamurchan and Mallaig-Skye.
If your bike doesn't have a good tank range you may need to plan ahead a bit and make sure you fill up whenever you can in some places; I didn't actually ever get to the reserve on the CBR6 (which does 140 miles or so to a tank) but it was a bit iffy once or twice, and bear in mind that petrol is likely not to be available 24 hours a day in little places (and in some places in the far north, you might find that Sunday opening in particular is *very* restricted). And expect to pay 10-15p a litre more in the Highlands and Islands.
If I had to pick a favourite bit of road from those I covered, I'd probably choose Ullapool to Durness and on to Thurso.
I believe that Paul49 has some hospital recommendations. Best to stay out of them, all the same.