1.) No, not really. There are ways to do everything you're asking for (interact with target, independent moving through arrow keys or whatever you choose) but there is no clean solution.

2.) You should explore the Jamba addon. There is an option in there where the master will automatically share any new quests they receive (if they're shareable).

3.) You can change the HKN script to adjust for whatever resolution you desire. It's very likely that the default script is not appropriate for your computer/monitor setup.

4.) The golden rule of WoW and multiboxing is one action from you causes one action from your toon. In other words, in most cases it is against the rules to cast two spells with one button press (or 4 DoTs with 2 button presses). It sounds like you need to work on your macros a bit and really think about what you're trying to accomplish with every button press. If you want your priest to cast mind flay every cast, and you want your warlock to cast different spells, then just keybind mind flay to both buttons for your priest.