I applaud your enthusiasm, but I have to take exception to the idea you can outfit yourself for $750 if you are going to market yourself professionally, especially for weddings.
I have done 3 weddings (and won't do anymore), and there are several on here who still do it for a living, and I doubt any of them (me included) would walk into a shoot with ONLY $750 in gear.
There was the mention of redundancy, which is imperative. There is the need for low light capability and IQ. There is the need for AF accuracy and speed.
Based on the many Pentax bodies I have gone though (K10/K20/K30/K5iis/K3), there is really only the K3 that is suitable for that environment. Its AF is leaps and bounds better than the K5 series. Yes, you CAN get away with a K5/K5iis, but your are tempting fate because the AF WILL let you down. I shoot wildlife, sports and other fast moving subjects in difficult conditions and I almost switched systems because of the AF issues on previous Pentax bodies.
I wouldn't do a shoot without a 50-135 (or 50-150 from sigma) and/or a 70-200 lens in the bag because, unless you feel like elbowing your way through a gaggle of cell phone shooters, and/or depending on the venue, you are going to need the reach.
A good flash well set you back 150-200 alone. The two above mentioned lenses are almost your entire $750 budget.
I guess what you want to do can be done, but to be brutally honest, if I were interviewing you for MY wedding and that was your gear list, I'd pass. No, you don't need a Mk(insert roman numerals here), or a D810, and no, a fancy camera doesn't make you any better a photog, BUT weddings are brutal to shoot. I'd never approach one without a complete kit plus back-up body because, yes you WILL need it one day. (It's also nice not to have to change lenses, just switch bodies.) You are leaving yourself open to non ideal results with such a minimalistic budget. And it's going to be those first few clients that will be the springboard for a successful career, don't short change yourself.
P.S.
Just a quick google search yielded several results, but here are a couple that list pretty standard and minimum gear:
What Gear Do You Really Need for Wedding Photography? | Light Stalking http://www.craftsy.com/blog/2013/10/essential-photography-equipment/
I think everyone mentions a backup body and around 3-4 lenses