The chimney at Faindouran Lodge bothy in the Cairngorms has collapsed. At present we're not sure how safe the rest of the building is. Therefore please do not use the bothy! The MBA will try and get out to survey it as soon as possible but it's likely to be the spring at the earliest before repairs - assuming practical - can be carried out.
The adjacent pony hut provides basic shelter in emergency.
Every blister I have ever had has come as a result of walking in wet feet, particularly on hard surfaces. So IMO the best solution is: make sure you have plenty of dry pairs of socks and, if necessary, change them several times a day. And whenever you get the chance, take a break and cool your feet off in a burn (drying properly afterwards)
Many years since I walked it, but a easy forestry track, followed by a section that isn't quite so obvious (but may be more so these days) which may be a bit boggy in places depending on the weather, and then an easy landrover track. I'd say it'd be pretty straightforward.
I've not walked it, but I understand the 'Monk's trod' - marked on the map as an ancient road - is an easy track. It runs from north of Rhayader to the north end of Llyn Craig Coch and thence over the high ridge SW to the head of the Claerwen Reservoir.
It's a route I've long intended to follow but not done yet. I think it'd be good.