-
There's no problem with going through private land as long as you're not damaging crops/going within a few hundred feet of dwellings. If there's an established track there it's especially a-ok, some landowners sign restrictions during hunting season but even that's not really enforceable legally as right to roam takes precedence.
Re: bothies, don't have personal knowledge of them-you might be better searching on a climbing or MTB forum. Bothies will be open anyway-some are not in a great state of repair though so damp/smelly and in some instances you'd rather camp, especially in summer. Also, you could turn up to find that they're full, and have to camp anyway so better having enough gear.
-
If you just stick the badger route personally i would bivvy/ use Loch Ossian Youth Hostel which you need to book in your case. or Hostel/Killin hotel for a bit more spendies.
SPeak with @mostly_by_bike he knows best on here for help.
Also as Ube says right to roam beats grumpy farmers.
This is day 2, so you can see that I'm taking a big diversion to get to the bothy. Downsides are: more miles, big climb, goes through a farm (bit iffy?) and I don't know 100% that it's still open.
https://www.strava.com/routes/20209429
Ideally I'd be able to stay somewhere halfway along the bottom of Loch Rannoch which is where my route initially turned south. Like Dall. But there doesn't seem to be anything there. Could just bivvy I suppose.