'99 323 is e46, correct?
If e46. I don't think there is an aluminum thermostat housing for this car. On an e46, the primary coolant thermostat is permanently stuck in the plastic housing so you buy a new housing. I am puzzled by the "map cooling, mechancal" part of that message though. I don't know what that means.
On a 13 year old BMW that has not had rigorous maintenance, you definitely want to buy a Bentley manual and some tools and get used to buying parts on line and spending your Saturdays in the garage for a while. If not, you will soon learn why many folks say that BMW stands for "bring my wallet".
First, the BAD news. If your cooling system is all original, you are due for a complete replacements of all the plastic and rubber parts in the cooling system, which is around $700 worth of parts.
The GOOD news is that nothing on your list is something that you cannot do yourself, and nothing on the list is anything that is going to leave you stranded on the side of the road. In fact, all of those things could be phantom codes set by a voltage glitch due to an old battery. I would clean the battery terminals and get the battery checked, then reset the codes and see if the codes return.
Remember that a code in the computer is not proof of a mechanical failure. It is simply evidence that the computer at some point received a signal that was outside normal parameters. Also remember that although OBD II is pretty darn good compared to earlier on-board diagnostics, it does not always point to the actual problem. Classic example is the "Catalyst efficiency below minumums" code. That code does NOT mean that you need a new catalyst. It normally means that you need new oxygen sensors. The sensor outputs are within voltage specifications so the computer thinks they are OK, but they are old and responding too slowly.
If Camshaft Sensor code returns: This is odd, I tried to look up the price and two sites don't show a camshaft sensor for your car. It has VANOS so it must have a sensor. Anyway, when you find one it won't be too expensive and these are generally not difficult to install.
If fuel vapor leak code returns. You may need a new gas cap. Unlikely to be anything else unless the car has been wrecked.
If thermostat code returns: As I mentioned, the reference to MAP cooling puzzles me. I am not sure what is going on with this code. If you really need a new coolant thermostat, I would urge you to seriously consider replacing everything in sight in your cooling system if you plan to keep this car a while.
If secondary air code returns: This won't affect the car, but you cannot pass emissions inspection with this code stored. There is a blower like a vacuum cleaner motor and fan on the passenger side of the engine. It costs about $230. First check to make sure that it is getting 12V from its relay right after a cold start. It should run for a minute or two after a cold start. If it has failed, it is usually because the check valve on the exhaust manifold has failed and has been blowing exhaust backwards through the fan. Remove the fan and start the engine. If exhaust leaks back through the hose toward the fan, replace the check valve. If you find water in the fan, replace the check valve. The check valve costs about $100. There used to be someone on EBay advertising that they would rebuild Volvo air blowers for half the cost of a new blower. BMW blowers are similar to Volvo. They rebuilt the blower on one of my '97 328s for $110. Seems fine. Replacing the blower and check valve is easy with basic tools. The check valve cannot be repaired. You have to buy a new one.
If the steering wheel code returns: If the stereo has been replaced, that is probably the source of that code. If not, I personally would not bother chasing that ghost.