Man, If I lived that close to Castle, I'd be completely broke! It's not as bad as you may think, to race there. It is very "businesslike" the way they run the races, so you need to pay attention to quite a few things, but if you know where to park and how to turn marshall, you know the hard stuff. Eric and Cameron are very cool to race with, well everyone is, actually. Stop by the store and talk to them about it before you come out. They can explain what you need to look for, and where to find everything. There is also a driver meeting before qualifying starts and they make it very "newbie friendly." I would start with just one class, though. It gets pretty hectic if you are trying to get two cars ready on your first race day. Sheldons is much more mellow. It's more like if you had a bunch of buddies bashing in a parking lot somewhere. There are much fewer cars, so it doesn't have to be so businesslike. A typical race day at Castle will see 150 to 180 cars. A typical day at Sheldons will see 40 to 50 cars. Give it a shot. Just be courtious when people come up behind you. Pull over in a safe spot and let them by. The most important thing is to be predictable so the other driver knows what you are doing, try not to hack people and say "sorry" if you do. Everyone wants to win and people understand that. As far as your setup goes, I think 30 weight will be way to light at Castle. You can probably get away with that at Sheldons, since it's more bumpy, but you'll traction roll at Castle if you have that little dampening. Everyone's driving style is a little different, so you kind of have to experiment. The Sprint is a good tire. If you only buy one set of tires, I'd buy mediums. Unfortunately, I don't have much track time on my TA03 to give you much advise and I only ran it a few laps at Castle during practice. I will tell you that the backend is way loose with the stock setup and stock tires. That's why I went with a harder tire up front and softer rear setup. The weight is balanced more toward the front of the F configuration, so the car will set up differently than a TC3. You'll probably want to run swaybars at Castle. There are usually a lot of transition turns like chicanes, s-curves, etc, so you want good transition or you'll find the car pushes as you set up for the next turn. You might want to bring the car in that you want to race and have Cameron or Eric help you get it set up. They won't have parts for the car, but they can help you with tire selection and shock setup. I would also get a ride height guage to you can get that set right. I would suggest running a non-Tamiya body so you get better downforce and lower cg. I love the scale of Tamiya sedan bodies, but they're not so good to race with.
I raced the TC3 all summer and just got the XXX-S. I like the TC3. It took me a little while to get the setup right, but it handles very well. I bought the XXX-S planning to run it in mod, but I think 3 classes might be a bit too nutty, since I want to race F1. The XXX-S is an awesome car. I really like it. I think the whir sound from the gears is what gives me the most wood! If you have not raced on a technical track before, you will probably not be too happy with the XXX-S. Some of the stock parts are not very strong. The TC3 seems pretty bulletproof. I've had some really hard hits and driven away without as much as a change in camber. The TA03 seems very strong, so I think that's a good car to race there. The only problem may be the availability of parts. San Antonio does a pretty good job of keeping Tamiya parts in stock. I haven't had the oportunity to directly compare the 3 cars, though. I had hoped to do this at Sheldons last week, but the race was rained out. I decided that I'm only going to run stock sedan, so I need to decide which car will be my primary car.
If you decide to race at Castle, I would stock up on some parts. Here's what I would recommend having in your toolbox as a minimum.
1 Race battery pack 2400 matched cells with 1.16V or 1.17V average per cell or you'll wonder why everyone is blowing by you.
2 "practice packs" The race pack will probably set you back around $90, so these can be cheaper. I use 2400 non-matched packs. You should be able to get good ones for around $50 and cheap ones for $30. You will use one pack during practice and the other during your first qualifier. After practice is over, recharge this pack so it's ready for your second qualifier.
1 complete set of upper and lower suspension arms. Usually a pack is good for either side of the car.
1 front and 1 rear knuckle
Gearing choices. I would start by gearing the car at around 6.00:1, but have pinions to go down around 5.00:1 and up to 7.00:1. You'll have to work out what tooth pinions you need. Castle changes the track configuration every race, so you will need to be able to change gearing to suit the track that week.
Tire/insert combinations. Since you're using Sprints, I'd stick with them. I would have 4 medium tire/medium insert wheels ready to go, 2 firm tire/medium insert and 2 medium tire/soft insert. When you put the soft insert in, brush some rubber cement inside the tire first so the soft insert sticks to the tire. It won't roll over on you that way. Keep in mind, this is what I would recommend as a minimum! I usually have much more than this. You will need to change tires throughout the day. It is rare when I keep the same combination all day long.
Shock support stuff. This is kind of a tough call and it may take you a few weeks to get this figured out. You have 30 weight oil now, so I'd get 40 weight and 60 weight as well. Generally, you'll be in the ballpark with one of those weights. I would buy a complete set of some brand of springs. I like Associated springs because they're not super expensive, they have a wide range of spring rates, their measurement is in lbs, so it makes sense and they fit most shocks. Unfortunately, they don't fit the Losi shocks without modification. I have no idea what will give the best results on the TA03, but it felt pretty good with the setup I'm running. If you want to be able to change shock oil at the track, buy a shock air remover pump. It's $30, but you'll be really happy you spent the money once you use one.
Servo tape. I like the Trinity stuff. It sticks well and isn't too bad to peel off when you need to.
Bring your soldering iron, solder, your charger and extra everything you think you might use. On race days, the shop sells out of the stuff you need to buy, so be prepared. Oh yeah, don't throw away those scraps of lexan when you cut out bodies. You will use them to make all kinds of stuff. You'll need to make a transponder mount that you can get to easily or drill a hole in your race body for it. Obviously, bring your tools. Make sure you have a few channels on your radio. I suggest a minimum of 3 so you aren't waiting forever for a frequency clip during practice. Make sure you have a good brush to clean off the dust and dirt from your motor and other moving parts. I use acid brushes since they are cheap and work well. It's good to have a couple extra wheel nuts and body pins in case you lose them. You will need one for the transponder. Generally everyone is very cool about letting you borrow stuff as long as your request is reasonable.
Hopefully I didn't scare you too much!
Seriously, though, if you are prepared, you'll have a good race day. Maybe race at Sheldons, when you can, to get the idea of how the heats run and how to read the results board to know which heats you're in, which channel you're on, which transponder you are using, etc. That's a good way to get your feet wet. I hope to see you out there!