Do I still need to do water changes in my tank?

of course you need to do water changes. I have a 50 liter tank and I do a 15% water change weekly. You should be changing at least 15% a week. The ammonia and nitrites will build up without water changes.

I have a simmilar size tank. I still do water changes, but only once every 1-2 months. This has allways worked out for me.

Yeah. Just to get some new water in the tank

Yes. Water changes add in minerals and buffer that are being depleted, as well as remove nitrates, etc, that accumulate. It sounds like a 10-25% monthly water change should be sufficient for your aquarium to regulate water chemistry. Continue to test the water and adjust if needed.

You definitely need to continue to do water changes (preferably on a weekly basis). If you're going to be negligant and refuse your pets the proper care, you should probably find a new hobby.

Partial water changes are always a good idea. As another said, the infusion of fresh water to the system helps to keep the water chemistry in balance.

Yes

It won't hurt. But if the pH if the tap matches the pH of the tank then you are probably fine.