Charging a stout keg

Well, to start, I've been brewing for about 10 years. Then, about 6 years ago, I dove head first into all grain, and never looked back. After a couple year hiatus, I finally have the time again to start back up. I told myself that I wasn't going to start until I was ready to keg, because I am tired of bottling. So, here I am. I am the type of person that over-researches EVERYTHING before I start something new, so I think I am up to speed on kegging. However, I do have one question. Are there any issues with charging a keg of stout with regular ol' CO2 first, then swapping in beer gas afterwards?

Actually carbing with CO2 and then hooking it up to beergas is the best way.

I carb to about 1.2 to 1.5 vols. And then hook it up to the beergas at 30-35 lbs.

Thanks for the response. That's the answer I was expecting, just wanted to be sure. Now, the only problem I'm going to run into is the unavailability of ball lock corny kegs. Some places on ebay have them, but I'm not paying $100 for one.