Reddit reviews Liquitex Professional Airbrush Effects Medium, 8-oz (5908)

You absolutely do not want to thin vallejo with any type of alcohol. It'll gum up the binder faster than you can dip your brush in it and in the end leave a worse finish. Water or some type of acrylic medium would work better.
http://www.amazon.com/gp/product/B001US2NQA?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00
This will last you for quite a few jobs since you only need a few drops at a time to thin and it will keep your pigments from being too washed out.

edit: I mean the airbrush medium incase amazon decided it wanted to link the other types instead.

Thin your paints further. Also try Liquitex Professional Airbrush Effects Medium instead of water to thin paints. I got it because someone here posted a link that had this stuff as a solution on how to thin metallics and not end up with a separated paint. Tried it on normal non-metallic paints and it worked fantastically. You can use it with or in a wet-palette too.

We'll start with your second question first.

I've pretty much given up on matte spray cans as I'm not entirely happy with any one of them, and most of them seem like they are just waiting to give my minis a coat of translucent white chunks. Overall, I've had the most success with Testor's Dullcoat. Sometimes it takes a couple of coats to get it to the matte level I want, but it's never given me the frosting treatment.

transitioning your colors can be approached in a number of ways. I've moved towards layering. That is, I create translucent colors using a medium added to my paint, and then build that up until I get the full strength where I want it. You could also use wet-blending, or even an airbrush. Check YouTube for tutorials.

You don't need airbrush cleaner, but it's cheap, lasts forever, and you'll want to have it around. You won't just use it to clean your airbrush, but anything you spill paint on, including yourself. It cuts through paint like nobodies business. So it's well worth keeping around.

I use GW paints and water them down with Airbrush Medium rather than water. Again, it's cheap and lasts freaking forever.

I'm using this as my thinner: Liquitex Professional Airbrush Effects Medium, 8-oz https://www.amazon.com/dp/B001US2NQA/ref=cm_sw_r_cp_apa_sbgRyb7YH3BXN

The reviews said it was being used as paint thinner and this is what I for after searching it, so I figured it was what I was looking for.

I would thin that paint a little further. Basically to a wash type style like a citadel wash. This way you have more room to play with the paint and can build up your colors more. So that being said if you have to use water I would bump it up to almost 5-6cc's or more. Now if you can I would recommended the two mediums below over water. I have used both and prefer the auto air over the other any day. But both are great. Reasoning - water just makes the paint break down and not have a great binding. Now the mediums will allow the paint to have that binding you need (flow) instead of just playing with colored water (tea).

They both work wonders and will mix with any of the water based model paints you have. I have used both with many lines of paint and have never had a problem. The auto air one is easier to use and a few drops will do the trick. The liquitex one I feels de-binds the paint a little easier, so less will do ya.

Let me know if you have any other questions. Always happy to help.

http://www.amazon.com/Auto-Air-Colors-Performance-Reducer/dp/B00CIEB28K/ref=sr_1_1?ie=UTF8&qid=1416461811&sr=8-1&keywords=createx+auto+air+reducer

http://www.amazon.com/Liquitex-Professional-Airbrush-Effects-Medium/dp/B001US2NQA/ref=sr_1_1?ie=UTF8&qid=1416461755&sr=8-1&keywords=liquitex+airbrush+medium

You will have a significantly easier time with a higher quality paint. I recommend the Vallejo line of paints from my personal experience. They make both brush and airbrush consistency paints. However, if you are set on using craft paint, I recommend that you thin them with a copious amount of Liquitex Airbrush Effects and mix them with a Badger Paint Mixer.