Rather than berate you on your choice of instruments, let me offer some constructive criticism. As Wes alluded to, there are a plethora of threads on equipment discussions that will cover just about anything you can imagine asking. The one major thing you have to seriously ask yourself is what are you doing this for?
If you want stuff on your car to look pretty and let other people know you are a chaser (which is fine), then don't spend that much time or money on equipment, but don't go around CLAIMING to be doing scientific research.
If you want stuff on your car that actually works and will tell you the temperature, pressure, winds, ect. to a reasonable amount of accuracy, but are only using it for your own edification, then spend a little more money, maybe buy one of the systems that contains all the sensors. They don't work that well and have a ton of problems with them, but for just knowing roughly what the temperature is doing or the fact that the wind just changed direction they'll work ok.
If you're serious about research, prepare to be spending some big bucks and a major portion of your time. Research quality anemometers alone run about $1000 so the equipment costs will jump pretty quickly. As an example, the NSSL mobile mesonet instrument racks run in the $10-15,000 range. Aside from the tremendous monetary costs, there is also a lot of time involved. Doing research with instruments is more than just buying the most accurate instrument and magnet mounting it to your car roof, there are a multitude of factors that one must consider to ensure quality data. The "S" shaped tube for example that a lot of researchers use has a lot of problems that make it a potentially bad system to use to house temperature sensors. NSSL has used this system in the past but will be using a newly designed system in the future. I could go on for DAYS about proper equipment use, but if your that serious about it we can talk more privately.
Main point: figure out what you REALLY want to do before you start buying equipment.
