There are a couple levers downstairs that you need to use to open the doors.
mapIn the graphics options within DD, you can change the darkness setting to 50 to increase the light range, and maybe bump up the gamma a bit to lighten the screen. This should make it easier to see levers, loot, etc.
The wishing well is a one time only wish; you can choose not to make a wish and come back later, but once you try to make a wish that is it.
You do not need the wish for any quest. The magic mirror quest can be solved before you leave Aleroth; there is a well on the eastern side of town that can give you a healing gem. If the healers have left Aleroth (due to completing the escort quest or getting an invitation to the castle), it is too late to go back; otherwise see
here.
You can 'cheat' to effectively re-do the wish, and get the same benefit as if you had tossed in more money. see
the Wishing Well (Spoiler)and use
iZakaroN's SaveEditor (or from
Kiya's site, with description)