the ELT should be picked up by D&D if you are in the air
An ELT won't be picked up in the time it takes any GA aircraft to glide to the ground.
The 121.5 transmission might be picked up immediately but it comes out at a very low power, sufficient for a range of some 10-20nm only. The 243 or 406MHz emissions are used for satellite-derived position fixing but they take minutes at best and possibly an hour or more to fix you. By all means do set off the ELT while still airborne but it won't do you any good until a fair bit later.
I would immediately set 7700 as that will be picked up by a lot of ground units, both ones we know about and ones we don't know about. London Control for example can see secondary returns some distance into France, at GA levels.
Minimum sink is usually just a few knots above the stall burble
Quite, which is why it can be a better idea. Single engine certification limit on Vs is 61kt, so the min sink speed might be 65kt. The Vbg, on the other hand, is 95kt for mine (TB20). The ratio of the two speeds is likely to be similar for other SE types.
If descending through IMC, it's a lot better to hit trees (or anything else for that matter) at 65kt than at 95kt. The difference in energy is about 2x.