Opinions vary about reducing the viscosity of Future for airbrushing. Experiment to find what works for you.
Bear in mind that it often looks terrible when applied, but levels out astonishingly as it dries and cures.
Thin (reduce) Future with 90% isopropyl. Do NOT use an acrylic retarder except in very hot or dry conditions.
The best cleaner for Future is actually a combination of equal parts Windex (with ammonia), and a 50% dilution of Simple Green in water. But if you clean promptly Windex alone is sufficient.