Regarding RTRs versus kits, I recommend getting a kit if you can afford it. Assembling your own car from scratch is a great learning experience. It will also allow you to hand pick all of your own electronics.

Regarding batteries, LiPos are worth the money vs NiMH. I'd suggest ProTek from amainhobbies because they're cheap and have a great warranty and customer service. I buy them, Thunder Power, and MaxAmps. They get more pricey in that order.

As far as a soldering iron, you won't need one for a while. You only really need them when you're putting together your own kit or changing out a motor or speed control. When you do get one, order a good one from a hobby shop. The ones at Home Depot usually aren't very good.

I'd suggest you consider investing in a good set of hex wrenches and a set of tires that the guys at your local track run (they usually all run the same tires). Tires have the single largest impact on performance. Adjusting your setup with a shock oil optimized for your local track is a good cheap upgrade.

Down the road I'd consider a good servo, a good ESC/motor combo, and a new radio, in that order.

There are a lot of servos to choose from. I almost always go with Futaba but Hitec, KO Propo, and JR are also good. A $50+ servo will have a really noticeable difference from the stock one.

For an upgraded ESC/motor, you'll be very happy with an LRP SXX/X-12 13.5T combo. Tekin and Castles are also good.

For a new radio I'd strongly recommend saving up for a Spektrum DX3R. It's fantastic radio and will allow you to bind up to 40 cars to it in the future. Each time you get a new car you just add a $100 receiver to it and you're set.

All three of these things can wait. Get some track time and see how much you get into it first. Most people get sucked in pretty quickly - especially if you're near a good track. And I know Portland has some good tracks.