2. Create a "User defined command" of the type "Internal command", Name the Command "ChangeSplitSize" or something.
In the command setup select "module" select "MultiCommander (Base)" and for command select "0/100" (or 100/0)
save it.
Create a shortcut to MultiCommander.exe (or edit existing one) and add commandline paramter "-AutoRun=ChangeSplitSize"
Now the command ChangeSplitSize will be run at startup.
BUT do not blame me if you accidentally do something in the hidden panel. 3. Not able to reproduce that.
4. For drag and drop there is a settings for it in Core Settings under fileysstem. Else you can create your one "Copy"/"Move" command from script and in the script tell it not to show a dialog and then you assign the copy key to that command
http://multicommander.com/docs/customcommands_list#mc.explorer.copyBy disabling the dialog then filters, plugins, and options can not be used.