Hi Vin.
EXP Autos Pro component work with Joomla CMS version 1.5/1.6/1.7 , when realease a Joomla 1.8 then I create version for this version.
1)Yes.EXP Autos Pro component have User Levels , in this level you can have varying price structures for each group.
You can see video
demo here >>>
2)Yes.
You can change fileds name in language file or create unlimited fields in params
3)This time I have backend deno only for version Joomla 1.5
4)No , EXP Autos Pro component no have this function .
You can use for this other extension from official Joomla site.