for the cities and avoiding redundancies, you could go to league structure (under global/game settings, i believe)
if you are familiar with either of those 2 options -- dB / spreadsheet -- both would work fine... the more complicated you go, you probably want the dB. you can do just about anything needed with a spreadhseet too and have it just as automated / 1-click operation type stuff too.
the db route is probably easier for what you describe, but a bit more technical? you have to do a lot more of the work with spreadsheets, imo. you could make all sorts of reports and queries to display the data you mentioned over time or whatever independent variable.
the csv files are just text files with a specified delimiter. when you import into a spreadsheet or source a databse, make sure to set the same delimiter -- think comma is default, but you can change those settings in OotP, too.
they'll be compatible with anythign you choose to do with it.
about the db settings in ootp -- you can reduce what is exported, if you have not already. you probably want to include "headers" -- at least as a reference to cut out, if it's a problem with impoting to excell/access type program. usually you can ignore first line etc, if needed.
as far as learning.. the type of stuff you'd be doing wouldn't take too much.. been long time for me, but you can find all sorts of sql examples online. how to select and manipulate is very straightforward. it will take time, of course... not unlike learning how to properly make a spreadsheet that doesn't require hands-on work each time you open it.
with only superficial knowledge from a college class 20 years ago, i was able to recently source a ~300mb relational db and make create soem sql statements to customize it a bit. i didn't recall any of the vocabulary, but i did know basically what had to be done. got user accoutns set up, it's communicating across my lan, but not with internet and working properly with a client.
the point: it may seem 'greek' the first time you read it sql statements and the like, but it's incredibly straight-forward stuff, really. it's likely covered in some forum or youtube video.