Welcome.
Not quite my kind of thing however you can work this out with btu's, from memory 1 btu is the amount of energy to reduce the temp of 1 pound of water by 1 degree over a certain time.
You can approximate btu's into watts, google probably does it.
So if you know how much water you have, how much you want to cool it by and how quickly you can back calc that into watts, which will tell you the size of cooler.
Tec's like other marketed items are probably well overated, plus the advertised power rating is probably the input power, so choosing something bigger is better.
Small tecs are cheap in 5's or 10's and 12v ones are common, pc processor heatsinks which have a built in fan can also be got cheaply, and pc psu's are inexpensive too, so a multiple system like this might be a good way to go, plus you could switch in and out heat pumps to control the overall power.