All GD addons are optional, but in your case you definitely need Location Manager, Custom Post Types, Events. You probably can de-activate the Pricing Manager if you only have free listings, but then you loose some control over options for the listings.
Although there are a lot of different Addons, they each have very little if any impact on the speed, because they all just complete one optional part.
Whoop is built for GD, so if you have any speed issues, they may be more server related than theme related.
You could replace Buddypress with our UsersWP, that may be a small improvement.
If you want to add drop down for the categories, you can add them as part of the WP menu at Appearance > Menu [I quickly added a few – delete if you like].
Bulk edit does not work with GD, and has been removed because it breaks a lot of listings if we re-instate it.
I doubt turning off the category count will make any impact, that would require some coding. Let us know if you want us to look a bit further into that.
Thanks