You will get a lot of different opinions of what to use and in the end you will need to find out what works for you.
My two cents: I have not tried the Alclad line yet, but I will. I have heard good things about them. I HAVE used Alclads’ line of paints though, and in my experience, they require some thinning. If I don’t thin them I end up with grain to the finish. I suspect the clear may need it too. But, not having tried them, I can’t say. For Alclad paints I use Tamiya lacquer thinner and it works great. Probably any decent quaility lacquer thinner will work.
Testers gloss and flat works well. You can buy them in jars for airbrushing, and they DO require thinning. Again, I use Tamiya lacquer thinner for that. You can also buy both of their offering in rattle cans.
I have also tried Humbrols’ Clear Gloss. This stuff works really well straight from the bottle. It is super thin, almost like water. No thinning is required. It is an Acrylic based product. Also, it brushes on and self levels really well.
The one takeaway I‘d like to give you is this. ALWAYS, test your airbrush mixture on scrap plastic first, and not on the model. By doing this you can catch problems before ruining all your hard work. I buy a box of white plastic spoons for this. A box is a couple of bucks at most, and it lasts me months. I prefer white because it is easier to see how the paint is going on verses a darker colored plastic.
Lastly... don’t be afraid to thin. It is a must in most cases. I find that I can generally get by with 1 part thinner to 1 part paint. It’s a good starting point and it is usually just right for my airbrush.