Hi Bourach. I've already been. The high level route in from the east was fine (see above map). From the road all the way up to the col there is a rough argo track which passes under the railway and has a bridge not marked on the map across the Allt a' choire Bhuidhe. From the col down to the bothy if you take the right line on the right bank of the burn the ground is fine if a little bit rough in places - normal corbett territory. I had a look at the route you suggest in part and it looks horrendous, I reckon anyone who has tried it would have ended up on the railway line at some point.
How do you get across the water at Arieniskill at the start?
On the MBA website it suggests coming in over the high ground from Lochailort - this is fairly new advice, as it wasnt there when I checked earlier this year. I dont know what that route is like but it's a lot longer than the eastern approach.
We carried in around 8 kilos of coal and a couple of fire logs. There was quite a bit of driftwood (if that's the right word) from the river lying about and we used some of that also.
As you say not many mice, we did hear one but only once.
If you want to walk in avoiding the railway completely, the eastern approach over the top is the quickest and easiest option I would say. Some fantastic views also and very enjoyable if you take the right line down to the bothy.
All the best.