Kevin,
You describe the shop that I currently have. I did use ICF's, 6'0 double doors, two windows, access into the house, radiant heat, sink with hot and cold water, and 200 amp panel just for the shop. I put up the ICF's myself, so the cost ended up being about the same as a standard poured wall, minus my time (Oh and you can vibrate some ICF's and pour as fast as the pump truck pumps). The garage does have floor drains but they are hooked up to the sewer. The down side is the drain pipes hang below in the shop. The shop walls ended up a little over 9'6". A dehumidifier keeps the humidity at 50% easily all summer and the temp. doesn't go over 74 degrees. In the WI winter the radiant floor heat and ICF walls create one of the most comfortable spots in the house (second only to in front of the fireplace).
Regarding water drainage through the floor isn't a problem. I used spancrete panels, then a rubber membrane (required by spancrete, but sometime left out by contractors because of the extra cost), then a minimum of 2" of concrete is poured over the rubber. In my case, 5" was poured around the perimeter sloped to 2" in the center at the drains. The spancrete is crowned in the center, so the edges need to be thicker to start and then thicker yet to get drainage to the center. Not a problem if you don't have drains.
I would highly recommend putting in 2 under slap dust collection runs down the centerline, 1/3 of the way in from each end, or one right in the middle. The table saw is the prime target, and you always know the table saw is going to be close to the middle of your shop. I didn't because I ran out of time, but I'm regretting it big time now. (If I didn't have radiant heat, I would seriously consider cutting up the floor and installing them now.) The dust ports don't have to be in the "perfect" place for future layouts. You can get them close and adjust layouts accordingly. I think it is better than having to put drops right in the middle of the shop. Even if you decide not to use them you put a cap on them and there is no issue. If they were to plug the runs wouln't be that long that you couldn't rather easily snake them clean. I would still keep runs along the walls above the floors for machines along the edges of the shop. Of course I have a 3hp cylcone, so a couple of extra elbows and longer runs doesn't really matter too much to me.
A couple of other thoughts that maybe aren't obvious. There are 4 steps down from my basement floor to my shop. As you mention your garage floor is lower than your house floor, this transfers to the floors in you basement as well. If you have a 9 foot basement and don't make the shop lower than your basement, your shop will probably only have 7'8" ceiling height assuming two steps from your garage to the house. So plan on some steps and leave room.
I wish my shop was a little bigger (dont we all). We have a 3 stall 25 x 34' garage, which means the shop is 24x33'. To make a little more room I put the tools in the shop portion and claimed a third of the basement under the house for lumber and general storage. With the shop under the garage and basically encased in concrete, virtually no noise makes it into the house. The shop itself really isn't noisy either because the insulation on the ICF's don't really let sound bounce off the walls. It's comparable or even quiter than my previous basement shop
The picture shows the spancrete being put in place. The view is from the house looking through the shop under the spancrete. The double doors are at the end with windows on each side.
Let me know if I can answer any specific questions.
Nathan