Hi Micehl
I can answer two of your three questions. the other one requires local knowledge but hopefully there will be someone out there with that knowledge.
In one of the descriptions it says: "There are three potentially difficult river crossings - usually these require a paddle, but in spate conditions can become impassable, particularly the crossing of the River Geldie." I already figured out what 'spate conditions' are, but what does 'usually these require a paddle' mean?
All it means is taking boots and socks off, rolling trousers up, and paddling through the water
Regarding 'spate' conditions', what are the most common times for these to happen? Springtime with snowmelt is obvious, but is there a specific time of the year when there are particularly heavy rains in the Cairngorms?
Spate conditions can happen any time of the year. In my experience, May, June and September are sometimes slightly drier than other months, but any month of the year can turn out to be the wettest, or the driest.
So, at any time of year, if I plan a route involving a river crossing, I tend to have a Plan B in case of a lot of rain. For example, last week I contacted the estate manager of Glen Lochay regarding crossing the river to reach the hill Meall Glas. After discussing the expected water levels with him, I decided to plan a different walk.
Hope that helps!
Tim