I've got the 16mm, 35mm and 50mm.
Love them all.
I would look at your budget first. Depending on what you are doing, $1,000 may be more than enough.
Where is your budget going? Do you need to rent/buy equipment or is it all going to crew and locations?
Experiment with the lights you have. The more you do that, the better you will get, do it enough, you can be a pro.
I would recommend against it if possible. Even though it's going to be your first short film, you never know, it could take off and go viral, and it would suck for that momentum to all come to a halt because a burger king executive notices a BK logo on a cup.
I got my GH4 new for $999.99, the only "catch" being it's an international version with no warranty.