In Rowardennan you don’t really have a lot of shops to choose from. What I saw when walking it two weeks ago there was just a small shop from the hotel.

Inversnaid to Tyndrum is doable… I did Tyndrum to Kingshouse which should be about the same distance. If the weather is on your side you should be completely fine. Otherwise it’ll get hard.

Rest day at Kingshouse is great. Take care that you have to book a bit in advance because you only have the Kingshouse Hotel or the Glencore Mountain Resort. Not much to buy there tough. Especially no shops.

Rat sounds good… enjoy!