If you're buying after market chargers, I don't think brand really matters, but that's just my personal opinion. I would rather buy brand-specific chargers myself.

Where the spare battery is concerned, I say it's a good idea - especially if you can find a charger that will allow you to charge the spare battery outside of the phone. That way you can have one battery in the phone and another battery set aside, charging.

I think haveing a spare battery is a good idea! You never know what can happen

Why do you want 3rd party chargers? Why not go ahead and buy chargers specifically meant for the Galaxy? As for buying an extra battery, I'd say go ahead if he uses his phone so much that he can't get through the day on a single charge.

What 3rd party charger is best and more convenient as a charger for the Galaxy Nexus?
How about in-car chargers too?
Does an extra battery make sense?
These will be gifts for a friend who uses his Nexus to make and cancel appointments on a daily basis. He is an outside therapist.