the probable downside with using water based stuff is that it will raise the grain and upset your already nicely sanded finish. Might be worth wetting the piece after initial sanding, sand again to remove the raised grain before you start colouring.
or, if you are feeling adventurous......
Stain with a dark colour to raise the grain sand back quite heavily before colouring again with a lighter shade. Unfortunately this doesn't work with Chestnut stains because they contain fillers which just block up the abrasive.
Its also worth mentioning that small areas can be coloured using permanent markers.
Something else to try is dipping a finger into paste wax, fingerprint onto the wood before colouring. When the colour is dry a hefty dose of wiping will remove the wax and its colourful coat leaving a, hopefully, agreeable hit and miss finish.
Rather than use an air brush seek out an artists diffuser [which is basically a mouth operated air brush] with practise all kinds of differing textures and effects can be achieved by blowing differently and from different distances. Far cheaper too!
And my strangest bit of advice?
Don't over-practice or over-think it.... just go for it. If you remain open minded about your destination you wont kick yourself no matter where your journey takes you.
Tarra
Brian