Glad we can be of some help and I agree you are doing the best thing by thinking it out thoroughly before you get started. It is very frustrating when you spend a lot of money on a small setup to then have to go and do the same again for another setup because it isn't big enough, way more economical and cost effective to get it right first time, though as you say you are starting with some of the stuff! I'm also sure that when I closed down the small one and moved the shrimps to the new tank that I probably lost half of the shrimplets as they were too small/young to be moved in reality but I really didn't want to have to run 2 tanks for a few months whilst I waited for them to grow - I had way too many anyway.
I can't be much help regarding the 'chiller' as we don't have hot enough weather here, in fact even the humans don't get that over here (except in expensive cars)? A lot may depend where you are placing the setup as well, mine is in a dark corner that doesn't get any direct sun. If it isn't likely to get too hot there for a while you can of course come back to that as a separate issue as it won't mean disrupting anything in the tank anyway should you decide to get one later!
You are probably best steering away from the CO2 as it is one less thing to set up and, as you, I have read a lot of reports saying it isn't good with caridina shrimp setups, though I have no actual experience with it, but why risk it.
Hope you will keep us informed/updated.
Simon