Hi Guys and Gals,
So, one day I got sick of 1964 brown paneling and crusty fixtures and I've started a basement bathroom renovation. I'm waaay past the point of no return, and need a bit of advice before I do the wrong thing. I apologize for all of the pictures, but hopefully they should help.
Here is what I am wanting to do:
I have to add the 2" shower drain, and I have to reconfigure how the washing machine drains, as it previously went into a utility sink where the future shower is going. The toilet and sink drainage already exist, and I don't plan on messing with it.
Here is what I have to tie in to, to add the shower drain:
The gentleman at Lowe's suggested I cut the cast-iron pipe off before the threaded bit, and use a hose-clamp/rubber sleeve to attach it to my new PVC piping. Is this good advice, or should I instead try to unscrew that elbow and screw in a male PVC union? I don't have a ton of room because the footer is right behind that elbow. Also I was told to not even start plumbing until I bought a backwater valve (which they don't carry), and placed it on the iron pipe. Good advice? I don't want to knock the Lowe's guy because he was helpful, but I couldn't tell if he knew plumbing or just thought he knew plumbing (I certainly don't know plumbing!

)This drain was previously for the laundry/utility sink, and now I plan on having both shower and laundry use the same main pipe. I am concerned about how to appropriately vent the system which leads me to the next picture.
Here is the vent stack currently in the room:
I'm fairly certain that I can't use that vent because it services the kitchen sink, which is directly above. I have no idea where that toilet ties into the drain, but I'm honestly going to try to avoid finding out.
I am thinking of the two options below. Is one better than the other, or do I need to go back to the drawing board?
Or
Thanks in advance for any and all help! I'd hate to take a shower ankle deep in yucky stuff!!
-Bobby