Bathtub drain help needed

Been reading these forums for a few months, but now I need help.

I'm replacing the tub in one of my baths. I took out a one piece fiberlgass 70's era unit, and I'm putting in a Sterling 18" tall, 60" long by 32" wide tub, then I will concrete board the walls and tile. See the picture below. This is what's left after I used a sawzall to get the tub out. Nothing would unscrew it was so old.

I want to put a whole new tub drain in for the new tub right down to the PVC, but that brass piece doesn't screw out I assume? (forgive my ignorance I've done shower bases before but this is my first tub!) My plan was to cut the PVC just below the brass, install a new coupling and go from there. Is that the correct procedure? If so, do I have to maintain this exact height so the tub drain hits at the right angle? Any advice at all would be awesome! Thanks!

Different tubs can have different rough-ins as far as height and left and right,front to back. If left and right and front to back lines up with the existing trap you can cut the 1.5" and start there. If it doesn't you will need to cut the existing p-trap off and start over locating the drain in the proper location. I'm leaning toward cutting the p-trap off and starting over approach as I like for things to line up perfect.....the 1st time.

Totally understood. I have the dimensions of where everything needs to go from the directions the tub came with, so I'll buy my drain kit, lay everything out and go from there. Thanks, that's the advice I was looking for!