Clay, IMO provides the best surface to race on. But it requires moisture so it's best suited for indoor use. Outdoors, in the sun, clay will bake if it gets dry. That would make it very difficult to make track changes. I should think that a good mix of clay & fill dirt will provide an optimal outdoor surface, and still allow you to easily change the layout. Check with your local parks department and find out if they use/used clay for any baseball/softball fields. But there isn't anything wrong with using what you have.
Yes, many facilities use sugar to treat a track - it helps hold the dirt together and can help starting a blue groove. Can't say I remember the ratio of water to sugar - you might try calling The Nitro Pit in Phoenix. They should be able to tell you (I just recently saw a photo from one of their recent track builds, there was a 100lb sack of sugar in the photo...).
AMB is the only system to use if you want to attract seasoned racers. We all have one or more PT's for for that system. And I know I would be VERY reluctant to buy something else.
Some personal gripes I have had from tracks I visited:
Drivers stand too close to the front lane. I was at one track where the front was a straight but, wasn't any more than 10 feet out from the stand. When your car came around the last corner, you had to lean out the drivers stand to see it. When the guy next you you leans over, they block your view - or yourself for the guy on the other side of you.
Too small a drivers stand. If you are going to have 12 person mains, make room for at least 15. Some guys are a bit over-reactive with their controllers, and some people just like to take up a lot of room. Either way, its much nicer if you aren't crowded. And put a roof on it! Shade is good!
Too difficult of obstacles. If you are going to put in something like a crossover, make sure ALL classes of vehicles can make it. It sucks racing 1/10 scale on a track where only the 1/8ths can make everything.
Track design makes marshaling difficult. Yeah, that long bridge that is 10 feet high is really cool, but if someone winds up wheels up on it, it takes forever for a marshall to reach the truck. Try to keep the design turn marshall friendly. Elevation change - especially radical changes - make for an exciting track. But that can also be dangerous for the marshalls. I was once at a track where there was a 15 foot elevation change and the down hill side saw a couple people hit by trucks that missed a big step down. Fun track to race, a nightmare to marshall that one spot.
Plan for RV's and travel trailers for large races. If you are going to have big races, plan on a space for them. Hook ups would be out of this world - most tracks want RV's to be self contained, if they allow them at all.
Oh, I'll think of more.
