Make sure you ONLY use either Mercedes anti-freeze, or the new Zerex G-05 formula. Everything else is BAD (well, except maybe Evans NPG but that's expensive). Seriously, don't cheap out on the a/f. If you don't expect to get temps much below freezing, I'd just use one gallon of anti-freeze and fill the rest up with distilled water. I also add a bottle of Red Line Water Wetter. Now if you live in an area that has harsh winters, like North Dakota or upstate NY, you'll need the full 50/50 or 60/40 concentration for maximum freeze protection. But down in DC, 40/60 should be *plenty*, and avoids having 3 leftover quarts of A/F hanging around!
BTW, I agree with the hot/cold thing... drain & flush coolant cold, drain oil hot. If you must run the engine for a coolant flush (like the factory citric acid procedure), let it cool down to an indicated 50C on the dash gauge, then spray the outside of the engine with water (from your garden hose or whatever), before sticking the hose into the radiator & water neck etc... that will help prevent cracked heads and/or gaskets. BT, DT, once I put a cold hose into a warm engine and was rewarded with oil in the coolant...!
I learned my lesson. Don't repeat my mistake!