Several "modules" in one Arduino

Hello,
what would be the easiest approach for this?
I have 3 different "sensor packs", each of which have ex. humidity, barometer, other (~3-4).

What would be easiest way to implement this kind of modules?
I was thinking of going with Arduino Uno for prototyping, but all other OK too.

In the end I'd prefer to use ATTiny though, so using same amount of I/Os should be important (?)

What would be easiest way to implement this kind of modules?

Install existing libraries and use them as is. Tends to work well.

In the end I'd prefer to use ATTiny though, so using same amount of I/Os should be important (?)

Not necessarily the same number as the Arduino, just make sure you have enough IO pins to connect whatever you want to hook up.