ZHR
regarding squats.
yes they can be a good help with strength for descending, training
Eccentric contaction of the muscle.
that is contraction against a lenthening force.
Its what happens when you brake as you descend.
the same action is produced as you drop into a squat.
There are a couple of reasons to do squats with weights.
1 - the momentum of running multiples the forces as you hit the ground on a descent (hence it can hurt alot the next day). To mimick this you need to add weight to your squats. (which can also hurt alot the next day, so build up gradually.
2 - lifting a weight forces you to focus on correct technique of movement.
an unweighted squat, you just do without thinking.
add 20 odd kgs and suddenly you become aware of the need to engage all sorts of muscles to maintain control, you have to apply a technique.
If you are goign to do them then I'd absolutely recommend you have a quick session with a lifting expert to get some coaching on correct technique.
I'd suggest you don't aim to build up to massive weights, instead aim to increase reps.
I've found squats have reduced post descending muscle pain. I used them this time last year in my BG build up (though dropped them later as my fell climbing increased). 3 or 4 sets of 10 reps at 40kg
More recently I've been doing lighter more dynamic squats - 25kg dropping quickly in and jumping out. First time I did 10sets 10 reps - too many, stiff and achey down hamstrings and back.
next time i did 5 sets 10 reps - still stiff
next time 3 sets 10 reps - ok
So from that experience I'd recommend you start with just 2 sets 10 reps with 20kg. build an extra set in each time you go (twice a week) build up to 10 sets. then go up to 25kg.
You might feel sluggish running the day after.
NB
warm up with a couple of sets of slow controlled squats (not dynamic)
and start with advice on technique