I don't have x10 but im guessing it's the same as x9.
To get an entity into the entity bank, go into entity bank and copy an entity's .fpe, open the fpe with notepad (you need to run it as admin) and replace the filepath for the model to your model, the easiest way to do this is by putting the model in the same folder and just wrriting the file name.
Then do the same thing with the texture unless you use multiple textures. If you do that just leave the texture blank and put all textures that you are using in the same folder.
You don't need to make the hitboxes your self, they are generated by fpsc. The default is box collision but if you edit collision mode you can get polygon collision to by setting the right number( i don't remember what it is)
Hope this helps
Srry about my english im from sweeden