Reactions with alkali hydrides are pretty instantaneous.  I'd have to recommend that you use something like methanol or iso-propanol instead of water since the reaction is kinetically slower and therefore less dangerous.  Always add the alcohol slowly to a cold (0 degree C) slurry of the hydride in a solvent like THF or toluene.  A lot of gas will be produced, so make sure your reaction vessel isn't entirely sealed.

This probably isn't the most efficient way to make H₂ either, but I suppose it would work in a pinch.

You can figure out how much you would need with the ideal gas law and some simple stoichiometry.

This is not the best way to maky Hydrogen.

Sodium metal is a lot more dangerous than sodium hydride though.

No I'd much rather work with lithium or sodium metal than their hydrides.  They are much less reactive in the air, i used to cut them up with scissors and drop them into my reactions without any trouble.  You need to be a lot more careful with the hydrides.

I concur.  Lithium and sodium aluminum hydrides require the use of a dry box to prevent ANY type of reaction from occuring, and if memory serves me correctly they are liquids as well.  This means that they can be spilled, thus increasing their surface area, thus leading to a potentially bigger hazard.  Sodium and lithium metal can be exposed to the air without risk of catching fire, and being in a solid form they are much easier to handle.

I use NaH on the benchtop all the time and I've never had any problems with reactivity in the time it takes to weigh them out.  I guess the type of reaction that use Na⁰ are usually just more of a pain to set up.  I always get nervous when I have to use elemental sodium.

My advisor says that he has never used K⁰ and not started a fire....