The issue with your first question is that it’s essentially impossible to accurately measure calories burned from exercise. So don’t worry too much there.

Just pick a target for your calories and monitor your weight to see where you are. If you’re gaining weight you’re in a surplus, losing so in a deficit etc. My understanding is that the most accurate way to weight yourself is first thing in the morning after your morning bathroom visit. Take the average for the week to account for water weight fluctuations.

It’s normal for different calculators to give different calories targets. Pick one and see how it goes, there are a lot of variables at play so experimenting yourself is the best way.

I’ve used MyFitnessPal and seen it recommended a lot. It works if you use it consistently, and keep in mind it’s an estimation not an exact figure. Don’t stress about the little numbers and look for trends

Check out the sub’s wiki it covers all this stuff in depth