So Should you get an i3, i5, or i7. it depends. if the i3 meets your needs and your requirements fit within the limits of that device the i3 may be for you. if you know or believe your processing or storage requirements are higher look to the i5 or i7 keeping in mind you can insert an SD card to increase storage but CPU, RAM, and base storage are fixed.
Then you need to think to the future needs although honestly I don't know if 4 or 5 years usage is feasible. I don't mean that it might not be useable, I truly just don't know and there's not a track record to judge by. Yes a Windows desktop/laptop of adequate specs should be useable for that long although most laptops I've had near that long either had the battery replaced or had very short battery life and you become a wall hugger. Would 4 GB ram be adequate in 4 years? Would it be better to say 4GB ram/128GB storage is adequate for 3 years after which I will replace with a current higher spec. model that's thinner, lighter, faster, with more, more, more.
The answers to these are not the same for everyone, it depends on the specific needs. What you want is another matter.