Designing Kitchens and Bathrooms - installing bathroom on cement slab. to cut or not to cut

I have a one story house on a cement slab and want to add a bathroom in a room that backs up to the single bathroom. I will be adding a corner shower, sink and toilet physically in that order. The cast iron vent pipe is directly behind the toilet in the original bathroom. The new toilet will be about 2 feet to the right of the vent pipe. there may be a cleanout pipe under the slab beneath new bathroom. How hard is it to cut into the slab and tap into the cast iron pipe? I know I will need a p-trap on the shower and it should decline to the drain, I assume I have to run it thru the slab and not the wall. How high will the shower drain have to be to run the drain pipe about 7 feet at a decline and how much room is needed for a p-trap? Any other info I may not have thought of is appreciated. I have read a little on the macerating system.

A couple of comments that may or may not apply to your situations. You said the shower, sink then toilet, physically in that order. Does that mean that the toilet is the first fixture you encounter when you enter the new bathroom from the hallway?

Generally, sink, toilet, then shower is the sequence from the doorway. If space is a consideration, I'd consider not doing the shower, just the sink and toilet.

I saw a buddy of mine solve a similar situation in a pretty cool way. He built up a "platform", basically framed a step up in the part of the room where the toilet was going. No concrete cutting and he did the whole the in a very short time. And since he was in California, where they pretty strict permitting laws, it could be restored to original easily if it ever came to that. He added about $20K in value to that house in about 4 days work counting the other things he did.

Frank

A picture is worth a thousand words.
You wouldn't be interested in doing a "one line" drawing of you house would you?

Facing the wall that the vent stack is in,(directly behind the toilet of the existing bathroom), where and how far, is the nearest perpendicular exterior wall and where will the new toilet be placed in reference to that?

Have you been to the city to find where your sewer comes on your property?