Bathroom renovation - walk-in shower. Need help with the procedure

Hello,
We have a house, the bathroom on the 1st floor is now about 17 years old.
Unfortunately, the shower is too small.
Now we wanted to install a WALK IN shower.
Now my rough approach:
Take off the old shower cabin, take off the old shower tray.
Put in a row of tiles at the bottom where the shower tray was, install the walk-in glass cabin, tile the floor slightly sloped towards the drain and roughly finished, right?
I wanted to remove the PVC floor outside.
There are old "tiles" on the floor. I wanted to install an electric underfloor heating with new screed on top. Then tile with porcelain stoneware.
Is that correct?
Or am I doing it totally wrong? The wall tiles are still okay. We wanted to leave them.
Just a large washbasin left, I can just replace that, right?

Hey
I can't really help you but I'm also very interested because I have to renovate a new bathroom, my uncle said today (he is a plumber) that there are often problems with the sealing of these showers and a lower shower tray that you almost walk into at floor level is better. So that there is an elevation, but only a very small one. My other uncle (now it gets complicated ^^) has it like that and I have to say it looks very good. Maybe that could be an option for you too.

But feel free to enlighten me :)

LieGrü