You'll have about 4" of backspacing total and everything else will have to go outward. So basically you could have as much as 1" of tire sticking out of the rear fender wells. Roughly.
The 17" wheels are not an issue at all its the width. You have someting like a total of 26" / 29" in height so 17" wheels is not a problem. You can not do that on the front. If you drop the Elky more than 1" in the rear then it could interfere with the wheel well but you could roll the fender well lip to give a little extra room. If you know how and are brave enough.