toilet rough in

I have a small bath thats part of a hollywood style bathroom. It doesnt include a toilet in the hall entrance. guests must enter the master bath portion to use the bathroom. I can remove the door between master area and drywall to make a solid wall and remove small closet so I can add a toilet.The toilet would need to be back to back with shower--of course my new wall would be in between. regular ply subfloor with master toilet about 5 feet away. is the rough in a big deal? what are the steps. venting?
crawlspace underneath. concerned about distance of only 12-14 in. from shower drain

What is below the floor? unfinished basement? Crawl Space? Slab?
Be better to draw what you have and what you want then ask the questions...
If you can Photograph the existing piping, all the better...