I’ve stopped in Meanach bothy, lovely location, the interior has been renovated by the MBA since I stopped there so it’s quite plush now, not that it was bad before mind. Never stopped at Staoineag but it looks a stunning place, hope the river isn’t too high for the stepping stones.
We rode(?) the Abhain Rath path in the opposite direction to what you are looking at doing so possibly more pushing the way we did it.
Edit: can’t help you with the Ben Alder track, the only riding I’ve done in that area is the Ardverikie Loop in the Scottish Wild Trails book. There’s quite a few marked tracks in the area that don’t join up 😈 they are probably stalking tracks from different estates rather than old byways or drovers’ routes. Might be worth having a look on geograph.org.uk to see if there’s any photos of it.