1) Faster zoning is probably more a function of general UI optimization, which isn't present while zoning if you use the default file. Most folks prefer to see incoming chat while zoning and the option to send chat once they've gotten used to the window
2) I'll double-check but the slider should be adjusting to the current quest on QH mouse over. Remembering what quest is active is a SOE issue.
3) It is currently safe to overwrite MainHUD.Map. The long standing issue with EQ2maps plugin support was recently resolved. I'll see what I can do about the "?" button in a future release, the scripting for this window is a bit convoluted. I'll look into the cropped map issue, it should be reverting to full size when closed. Both the Inventory and Map windows use an external "Dock" window to control main window placement when shrunk. You'll need to open and reposition the dock if you want these windows to dock in a different location.
4) Yes mousing over the center of the minimap is intended to resink it to the main map. You should be able to replace the Help button for this window with one copied from a window that already activates IC.
5) I'll have to dig up an old version without the performance buttons. Untill then, you can remove the includes from that file and adjust the window size.
6) Yes removing custom items from the start menu should only require deleting those items and adjusting the window size and object positions.
7) The "Take all coin" button was removed from 8.2, SOE never enabled it. In general, lists that include an icon use one row mockup for all rows, so dynamically adjusting rows in game isn't really an option. You should be able to adjust the mockups if you prefer something different. The fav files are no more complicated than any of the other xml files. Use Notepad and you'll be fine. Each is basically 1 menu and its datasource. Each Data object is a row in the menu with all its filter settings. There is no limit to the number of items in a menu far as I know.
8) see #4. I'm hesitant to replace every "?" button with IC and loose access to the standard help.
9) Correct. I renamed the main file to ensure it won't be replaced by the standard IC files. Socials and display profiles are the only other things I had to directly tweak.
10) Enter and esc functionality has been added to a buncha stuff, but those 2 are the only windows likely to affect how you play in any significant way. Tradeskills use it for the combine screens, so you'll want to avoid starting chat with Enter while crafting. If you do find a window you'd like to remove this from, open it in Notepad and deleted isdefault="true" and/or iscancle="true".
11) The old skills and society windows are currently unused and I don't think are included in any other files. Should be safe to delete them. Hud slider might be used for something else in the future. I did look at the character select "Next" button and so far haven't figured out what the problem is. I'm gonna run some tests with default to try and figure out what the deal is with that. I'm not convinced its any different in default. Could be the custom UI size I use is resulting in the text being shoved off screen.