1.) What's the keybinding of your delete key ? Sounds like it's bound to 'delete-char'.
Check 'Tools>Options>Redefine Common Keys' for an approriate binding.
2.) ditto
3.) You could use v12.02 and the new comment / uncommnet line/block feature

BTW: What version do you use ?
Or you can use the 'slide-in-prompt' resp. 'slide-out-prompt' commands on commandline or via keybinding.
Additionally there is a 'block-insert-text' command.
For all of these command a block/line selection is required.
Good luck,
HS2