ahh thank you for explaining
For this kind of thing I try to bridge rulings with RAW, since I think a lot of the things that make these kinds of scenarios viable would be cans of worms unto themselves in my actual games.(B) They're using longbows so 125' is an absolute minimum, but they'll take as much as they can get, scattering in different directions if necessary, although if Fog Cloud is allowed to grant advantage to all four archers at once there's some incentive for them to try to stay together. (Ergo, tactics depend partially on how the DM runs heavy obscurement.)
I'm game for it, if you'd like to do so then please provide the full blocks and buffs involved when you have the time and any feeback regarding the set up before game start.(C) IMO that's not such a big deal, since Phantom Steeds can already get 220' movement easily (100' + Longstrider + Dash) and more is possible via e.g. Haste if needed, although scattering in different directions may make Greater Invisibility a better use of concentration. But you're right, Dashing is a good strategy for her, one I strangely forgot about, maybe good enough to make playing the scenario out in detail worthwhile. Let me know if you want to.
Ahh they're like high fantasy traffic cones, that's actually pretty amusing.(D) Since you can't end your movement in an enemy creature's square, the elementals are there to restrict where she's allowed to end her movement and make it harder for her to pursue the archers.