PVC into Cast Iron DWV Pipes

Hello,

I am a new user and first time poster who found this board two months ago in search of info. for planning a first floor bathroom remodel and need some advice on a DWV question.

I have attempted to add a photo from our crawlspace showing what we have to work with:
#1 is our PVC tub drain
#2 is a copper waste pipe for our toilet (there are two small "arms" that run off this copper pipe and up/into the wall; I am unsure where they go. One is shown in Inset Photo A. The left arrow points out the "arm", the right arrow points where the pipe enters the bathroom floor)
#3 (wrapped in tape) & #4 run parallel to #2, beyond it, then into/up a wall (see Inset B.)
I was unable to visually locate/figure out where our lavatory drain connects to all this (It is to the right of our toilet).

At this point, I would like to remove everything above the two "main" cast iron hubs/bells, and replace with PVC DWV pipes. Right now, my big questions are:
01. Would this be the smartest approach? If so, what is the best way for me to connect PVC into the hub/bell?
02. On our second floor, above this bathroom, is an empty room my wife and I would like to turn into a full bathroom, but not anytime soon. Is there anything we can do during this first floor remodel to facilitate remodeling the second floor when we can afford to?

Any insights would be greatly appreciated.
Thank you,
Dave

Where the tub drains into the Cast iron tee...
I think that that is a saddle tee....
Not sure if that is code compliant in that use anywhere in the US....

just cut it all out and replace it... looks like a nightmare