Hi, Rick -
By two stage I guess you're describing double action, the ability to regulate the amount of paint spray by moving the trigger back and forth. There are so many really good quality airbrushes available, several are quite reasonably priced at about US $70-80, others can be upwards of $250-300.
I use Paasche, Iwata and Badger, all work well, it comes down to the users informed decision based on personal use. I now use almost exclusively Badger, for me it's about 1) spray quality, 2) ease and comfort of use, 3) durability, 4) ease of cleaning.
Although I have about a dozen in the collection, the two that are used nearly 100% of the time are the Badger 100G and 200G. Both gravity feed internal mix, the 100G is double action, the 200G is single action. Watching out for sales, the 100G was about $70, the 200G was about $50. The dealer I use is USA Airbrush, excellent service and reputable, great source for parts when/if needed.
Almost everything I paint is done with a medium needle/nozzle set, rarely a large, sometimes the small set for finer borders of camo. Very easy and simple to change, 60 seconds if you take your time. I use exclusively Tamiya acrylic, easy and consistent. I find little to no need for surfactants like Liquitex, but your use may require them. If so, they work well through an airbrush.
For a compressor I use a California Air Tools, sort of overkill, but so efficient, quiet and durable. $180, likely the last one I'll need, but if this one should cash it in, I'll replace it with the exact same one. Model is 1610A, twin cylinder, large tank. THE BEST I've ever owned, plenty of power for garage/tools work too.
Can't think of much else, I second the advice to check Don Wheelers website, just Google the name and you'll find it. Don is pretty much the recognized all around information source, for all things airbrush. You'll find detailed info about nearly all of the airbrushes and models available today, I highly recommend it.
Best of luck with your search.
Patrick