First, you need to consider your water. You can do this without a meter. If you buy a water report from wards, you can find out how badly you need to mess with your water. A meter is nice, but I think you can get "close enough" with your water without one.
A whirlpool chiller is great, but the big thing is getting a pump. Gravity works ok, but a pump makes it almost hand's free, instead of having to rig up a gravity stand and you just run it until it's done, as opposed to getting what you get when it's done draining.
Both have their advantages, but I'd probably go with pump and whirlpool chiller first, since I think water can be worked with to a certain degree without a meter. Nice addition either way, though.