I was thinking I'd use the aluminum and silica (for the viscosity) though as opposed to replacing the silica with alum.

Opinions on epoxy additives vary. My opinion is that it's the silica that's the essential component in those hull coatings, if you are looking for abrasion resistance. Silica and epoxy makes a very hard (try to sand it once it's fully cured, you'll be a believer) coating. Graphite doesn't make a boat any faster in the water, though perhaps it may (though I'm not convinced of it) make the hull a bit more slippery on rocks. It tends to 'soften' the epoxy/silica. If you want a hull that's slippery, get it very smooth and then wax it. The wax doesn't reduce the friction of the water but it helps to keep dirt and weeds from sticking to the hull. They do slow you down a bit.
WEST started selling graphite as an additive to make low-speed bearings (rudder stocks, etc) and then it seemed to become popular as a hull coating additive after that, because folks thought it would make boats faster in the water.
The aluminum should look pretty sharp on your hull; be sure to post some pics of the results.

If you want the 'black look' on your hull, epoxy/silica with a good dollop of System Three Black pigment (pigment ground in epoxy resin) will give you a nice shiny hard black result. That's what I use when I'm bonding hatch rims to glass; it looks good.
Just my 'two cents worth'... :-)

BTW, it would be worth your time to make up some samples (on plywood) and drag them down the road with a weight on top. I think somebody did some tests like that (Vaclav at One Ocean , or ??).