Hi Diovani, and welcome to the forums!
Yes and Yes!
But there are a few things to keep in mind:
I assume you are already checking out the
free version of Platform Builder, yes? If you upgrade to Platform Builder Pro, the playable character's sprites are changed from character setup. All other sprites are changed from the "sprites" page of Game Setup.
Sprites are uploaded from sprite sheets, and these sprite sheets can be downloaded from Platform Builder if you are using Pro. There are sprite sheets for enemies that already exist, and a couple sprite sheets for any new enemies you may wish to draw up. All in all, these blank enemy sprite sheets allow you to create up to 24 small (32x32) enemies, 12 tall (32,48) enemies, and 9 large (48x48) enemies. These numbers may increase if I find that there are many users who need it.