I've always played heels-up on both hat and kick, and that made transitioning to double kicks a lot easier.
I run with my throne quite high- I've never understood how players can do it with their thrones way down in the weeds. My throne is high enough that my thighs are just slightly downhill from hips to knees- my knees may be 1/4"-1/2" lower than my hips, and my thighbones are just the slightest bit downhill. I find throne height to be absolutely critical for endurance and comfort, so tune the hell out of that adjustment before you try to go further with heel-up technique. If you're used to having your thighs running *uphill*, it'll take you a lot of doing to change your positions!
Somewhere I read years ago that the thight bone should be exactly horizontal, but that always felt too low for me. One size does _not _ fit all. So adjust until you find the sweet spot.
Once you have the throne height dialed, and you have some practice time in, you can hover your heels about 1/2" above the pedals all night long. You touch down every so often, but you never plant your entire leg weight on the pedal. It's like learning to ride a bicycle really efficiently for racing (which I used to do, back in my misspent youth). On a racing bike, you never let the weight of your leg get pushed up the backstroke. You _lift_ against the toe clip and produce power back there as well (it's called "pedaling in circles, not squares"). You use those muscles to float your feet for heel-up: the ones you'd use to produce power on the recovery stroke on a bike.
Needless to say, the throne seat itself is critical as well: an uncomfortable seat makes this nearly impossible. I learned to do it in the 70s on an old Rogers round, naugahyde throne (the slick naugahyde made for a lot of sliding around!). Then, a few years back, they came out with the bicycle-style seats, and I was *instantly* more comfortable. Try different seats until you find one that you don't have to _think_ about to maintain your position.
Toe position is a function of your pedal design, your preferred spring tension, and the balance of speed versus power you need in your playing. I've always played with a heavy hand, and I've never been a serious contender in the speed department, so my style probably won't work for anybody who wants to be Portnoy (although it is the way Billy Cobham does it). I put my normal toe position about 2" back from the beater end of the pedal, and when I need to do quick double or triple-kicks on a single pedal, I do the second and third strokes with a slight slide forward towards the beater end of the pedal- maybe 1/2" per stroke. For normal work, I don't do any slides- just when I need speed.
On the hat, this lets me do heel splashes easily, and if I'm doing syncopated open/closed work, I can still knock time by dabbing my heel down without affecting the open/closed stuff.
Best exercise for learning the two-heel float thing, endurance and conditioning- paradiddles and double paradiddles. Pretty much anybody can do reasonable right-left-right-left singlestrokes with just a little practice, but getting smooth paraddidles is vastly harder with your feet than with your hands... Cobham used to do pages from Podemski's snare method with his _feet_ (or between any foot and any hand, as well) back years ago, on the seminar circuit. Made me freakin' sick.
Your mileage may vary, though. All this shit works for me, a fat old slob who was never a contender in anybody's book, so you can expect different reults. Watch your favorite technical drummers, check out their seminars, and try things.... I'll almost guarantee that the throne will need to be higher than you think, and that'll probably require a rethinking of the whole kit to help you play with neutral balance and a good, stable, upright posture. Hell, posture may be the most important thing, come to think of it- you can't do this and slouch!
Hope that helps, anyway.
