a few more questions:
Most tub trap arms are run in 1-1/2"-if my bathtub drain pipe is 2" does the p trap off the tub need to be 2" or can it be 1.5". the vent is 1.5" does this matter?
It can have 135 degrees of change,- can a toilet 4" waste pipe have a 90 degree bend in it laying horizontal and if so does it need to be a long sweeping one
Your inspector may allow medium bends after the vent on the trap arm, but not on the rest.
Long turns and 45's.
If you are cutting into a cast stack, use a cast iron no-hub fitting with shielded no-hub couplings.- when cutting a Wye or T into a cast iron main stack, what fitting is required if the line coming in is ABS 2 or 3". do i need a cast iron fitting?
You will spend less money that way, it will look nicer, and it will support the stack better.
The vent doesn't care.- does a vent care if it has a 90 degree bend in it versus two 45's
Don't use lav supplies for a shower.- can i use flexible water supply hoses (typical for sinks) to supply a shower? thinking from the shutoff to the actual shower control so a run of 10" or so - otherwise i have to reroute the existing copper
You will need to support the shower valve in the wall solidly, once that is done, you could run PEX, which is flexible, and rated for inside the wall use.