One small but important comment: if buying multiple cordless tools, buy a brand that you can interchange the batteries among all of the tools. Spare batteries and a backup charger are also important so you can keep going and charging. I believe they have LI-on 1 hour chargers out now.
Milwaukee lithium batteries, and everyone else's I assume, charge in more like 15-30 minutes for both 18V and 12V batteries. This means that even in the most extreme use case you can run continuously with only two batteries.