If you are just brush painting with them, just regular tap water or distilled water (about $2 a gallon here) works fine. If you are going to thin for airbrushing, its hard to go wrong with their own thinner, while you can also use distilled water when thinning for airbrushing....their thinner makes short work of it.
For cleaning...again, if you are brush painting, regular water is fine, for airbrushing, Vallejo has an airbrush cleaner that breaks down the paint and makes it easier to clean the airbrush....I think it also has a little lubricant with it....so once your AB is clean...it is automatically lubed as well.
For a good conversion chart, check out the "Ultimate Paint Conversion Guide"
http://www.paint4models.com/ 
