I’m an old git and have been touring Scotland for quite a long time. Ist trip up the West (wet) coast in 1983.
- April May June is a great time of year to go its normally Drier in Scotland in spring (as it is in N.Ireland were I’m from) but even if sunny it can be very cold esp. at night (frosty) so if your using hotels and B&Bs you will be grand. Camping could get uncomfortable. As an example I ended up riding through snow from Invergarry to the Kyle of Lochalsh on Mayday 2017 😊
- What you will be able to cover depends on weather you want to enjoy the roads and scenery or whether you want to sight see. I tend to be a enjoy the roads and scenery sort of a rider so don’t stop that much at sights so to speak
- If you do the NC 500 I would miss the east coast section and go up through the middle of the top of Scotland via Bonnar Bridge Lairg and Altnaharra. At Altnaharra you can chose to ride up past Loch Loyal and end up in Tongue (who doesn’t like tongue😊)or a very narrow road past Ben Hope and the ancient Broch Dun Dornaigil.
- You can’t go wrong with the west coast and Islands for scenery. Get off the main NC 500 when you can For example the route through Lochinver down to Ullapool is a lovely (mostly single track road Diversion).
Starting in Newcastle I'd take the inland route and head towards Kielder. There is a (toll) dirt forest road there its very easy (last time i did it on an r1200rt

) Moffat is not far away and the Buccleuch hotel is a great place to stay. Dave the owner is very knowledgable about the local roads. If crossing the central belt. I'd recommend two routes
Take the minor Single track routes towards Gourock and take the ferry across the Clyde to Hunters Quay From there you can head to Strachur and Inverary then up towards Dalmally. You can take a coastal route north from here if you turn left toward Connel or the more senic route over Glencoe if you turn right. There is a lovely single track road along Glen Orchy that takes you out onto Rannoch moor. An alternative is a lovely quiet single track road along the side of Loch Awe that runs south of Oban. Which you can use to get to Oban for the Island ferrys or you can head north towards Fort William avoiding it across a couple of mostly unused moorland roads.
Or thread minor roads together between Glasgow and Edinburgh and end up in Bonnybrigde at the start of the B818 (Crow road I think) then head to Aberfoyle and the Dukes pass. From there you can turn right toward Killin and head north via lovely minor roads past Ben Lawers dam and Tummel Bridge before heading west at Dalwhinne towards Spean Bridge. Turn right and you can go up through Crainlarich and Tyndrum to head over Glencoe and join the rough route above. Whatever you do you will have a ball Scotland and Ireland if you ever get here are great countries for motorcycling. A few photos of past exploits to bore you with

I've toured with the bike in Scotland at least 30 times and I'm not bored of it yet.
The top of Bealach na Ba April (easter 2005)
Bit easier further down!
Kylesku Bridge 2002
View of Ben loyal from the Kyle of Tongue 2004
Commando Memorial Spean Bridge (missus in the background lurking)
Lovely backroad from here through Gairlochy and down to Corpach (missing Fortwilliam) good route coming from or going to Mallaig or to access the Moidart peninsula.
Touring on a gsxr600 Glencoe April 2005
Swing Ferry Glenelg to Kylerhea
Talla Reservoir Borders Nr Moffat May 2022
Mull road to Fionnphort Oct 2022
1300 mile 2100km trip from 2008