Several questions (new to Bodhi)

GRUB does allow various customization. You can always have it boot a certain choice by default or boot previous by default. You can control if the menu is displayed or not and for how long, or how long you get to push Esc to bring it up. You can even theme it if you want.  Most of this is done by editing /etc/default/grub then running the update-grub command to apply the changes. All of this should be in standard grub documentation tho, nothing bodhi specific. If I wanted to edit those config files I'd lookit up too, probably with a web search like "grub2 set default" or something.

There is a tool for it called grub-customizer if you dont want to mess with config files yourself. 

That command will install it for Bodhi 6 (as it is provided in focal repository).   For Bodhi 5, if you want to do that, you'll have to add a PPA first, then above command willw ork.