Basement bath rough-in help needed

While I plan on hiring a licensed plumber to do this work, I'd like to make sure I understand the requirements as well, to ensure the job only needs to get done once

I have an existing basement bathroom which I need to tear into, to have some broken clay drain pipe repaired. Had the drain camera inspected and while 90% of the line is in perfect condition, there is some root infiltration right near where it ties into the new drain of the house, under the existing basement bath. I wanted to remodel it anyhow, so here's my excuse.

It's a small 4 x 7 foot space (finished floor space) and I plan on putting a 36 x 36 shower, toilet and small 18" wall mounted sink, (30" for toilet, 18" for sink on one wall, shower on opposite wall).

I haven't torn into the drywall yet, so I don't know for sure how things are vented, but everything is working just fine now (toilet and sink only).

I've created a diagram showing the location of the main drain under the floor and where I'd like to locate the toilet flange, wall sink drain and shower drain. I'd like to confirm the best possible configuration for connecting these to the main drain, with venting requirements.

Also, there is a clean-out at the bottom of the main stack - is it possible/allowed to 'extend' this clean-out port to bring it along side the shower, so I can have easy access to it? Or possibly I might need to install another clean-out on the horizontal drain under the floor with access beside the shower?

Any input provided would be more than welcomed. I have to confirm there is a proper vent running down to the basement to utilize - if not, I think my only option would be an AAV vent perhaps up in the cavity between the shower and main stack, made accessible by an access panel. I plan on keeping this area open and accessible, perhaps with narrow shelving for toiletries, rolled up towels or the like. I'll have about 8 inches between the 2x4 wall beside the shower and the wall of the bathroom.

Hopefully the diagram makes sense and people understand what I'm looking at doing If I'm within a certain distance from the main stack, do I need to vent each fixture? I.e. if the new 2" shower drain is say 4 feet from the main stack, does the main stack provide the necessary vent for the shower?

Where is the "other" post? IF you are going to have a professional do the work, you do NOT have to know how he is going to do it, assuming he is competent. IF I were doing the work, I would tell you to show me where the sink, toilet, and shower were going to be, then tell you to go see a movie or something, while I installed the plumbing. IF you tried to tell me HOW to do it, I might ask you, "If you know how to do it, why did you call me?"

The 'other' post is #2 above. I posted the picture again as it didn't appear to work the first time, but then it did show up, and I can't delete the 2nd post. So there you go.

Not sure what the point of this forum is if not to ask questions like I did and seek knowledge and advice from others, regardless of whether I'm doing the work myself or paying someone to do it. I, like 99.9% of people out there, don't have a regular trusted plumber that I would put blind faith in.

If I was having surgery, I'd want to know what was being done, what should be done, what others think, differing opinions... I wouldn't call up a surgeon from the yellow pages with good references and then just hope for the best.

This is in my basement, under concrete, never to be unearthed again. I'm putting a bathroom with heated marble floors on top of this, and don't want to have to do it twice. I'm doing all of this because the idiot previous owner who tied the new plumbing into the old clay drain pipe didn't have it inspected, because if he had, he'd have seen the cracked pipe 3 feet down from where he connected to it and could have repaired it at little to no extra cost. A few extra feet of pipe and digging.

So yeah, I'm keen to get opinions / knowledge on what the best configuration for this setup might be, so when I get a doofus plumber in who tells me I don't need to worry about vents for example, I can move on to the next guy.

This and other forums are filled with 'the last guy made a mess of it and now I need to fix it' threads. If all professionals did it right the first time, this site wouldn't exist.