The UNO/NANO/pro-mini all have about the same I/O and all use the same chip. all run at the same speed.
we often recommend the UNO because it can accept shields and is a bit easier to work with because of that.
From what you told us so far, I would recommend an UNO with an RTC shield. it will plug in and have a real time clock (RTC) that you may not care about, but it will also have memory and an SD card slot.
it will plug right into the UNO and from there, you can find lots of people who have used it. there is a small breadboard area in which you can wire up some resistors and such.
you should be able to get close to what you want with that.
once you get this working, and want more accuracy, or more resolution, let us know. I don't want to overload you with that just yet.