First the bad news: your button arrangements will not be available anymore for v11 because v10.20 saves the toolbar configuration in the registry while UltraEdit v11 has a completely new method for handling menus, popup menus and toolbars. They are now stored in plain text files - *.mfg for main menus, *.pfg for popup menus and *.tfg for the toolbars. These configuration files are always stored where the current ini file is stored. Your buttons are not lost for v10.20c, if you switch back to v10.20c temporarily or use it simultaneously.

All other settings will not change during the update because they are only complemented with the settings for the new features.

Attention: Don't click blind on the OK button during install. Read carefully because on every update the standard wordfile for syntax highlighting and the standard taglist file will be updated with a user selectable method during installation process.

UE v11 only saves a view settings for update checks in the registry if you have not specified in the configuration dialog of v10.20 to save everything in the registry.

Can I run v10 and v11 simultaneously?
Yes, you can if you move all configuration files from default user data application directory to the program directory of UltraEdit before installing v11 into a new directory not overwriting the existing installation. You should create the new UltraEdit directory manually and copy the configuration files from v10.20c to the new directory so your settings will also be used for new v11 before running the install.

See also following forum topics:
How to transfer configuration settings to a new PC
Basic.mfg in another directory???
UEdit32.ini in a different location than user or windows
Running UEdit from a usb key

And many further articles from me can be found about configuration of UltraEdit.

But I think, after moving the configuration files to the UE v10.20c program directory it would be easier to backup this directory and update the directory with v11. Now you can always switch back to previous v10.20c by just renaming the UE directory of V11 for example to UltraEditv11 and the backup in program files directory from UltraEditv10 to UltraEdit while no UltraEdit is running. This is the method I use to test something with an older version to help users here in the forum. I for example have
C:\Programs\UltraEd
C:\Programs\UltraEdv10_20
C:\Programs\UltraEdv10_10

Note: After installing v11 you should read syntax.txt in the UltraEdit directory for new syntax highlighting features and their settings in the wordfile.

You will have to do the arranging manually once V11 is installed.

Everything you listed can still be customized, but the toolbars of v10.20 are not automatically converted from the registry to the toolbar configuration ASCII file during the update process.