Character Level Power Increase Question

I was wondering if your character level is used to determine how much damage you deal or damage you take vs monsters alone.

So assuming you don't use any passive points between level 25->26 and fight the same monsters, are you more powerful now? (also you didn't level any gem skills)

You get life upon levelling up so yes, you will be marginally more powerful.

You only gain life, mana, and evasion rating. Everything else, barring passives and gems leveling up, is exactly the same.