New to BBT!

Hello! I just bought my first basal thermometer today, should be delivered in two days. I'm still new to the basics, but can slightly understand charts. I do have a few questions though.

1-when to temp?

2-does it matter what part of my body that I use to temp?

3-do I have to start on the first day of AF, or can I start a little later?

If anyone has advice, I'm open to hear it!

My current method is checking my mucus, which has been reliable, checking my cervical position, and taking opk's which have also been reliable. Thanks!