Any problems with my drain plan

[Jacob]

I am remodeling master bath and want to make sure my drain plans are correct. I am mostly concerned with proper venting. The attached picture will give a general idea of my plans. The original drain is 3” cast iron. I plan to convert to 3” pvc with Fernco coupling. Then branch off of this with a combination wye reduced to 2” to the wall between the sink. From here use a long 1/4 bend up the wall and sanitation double tee reducing all three to 1.5” for the two sinks and vent. Continuing up the 3” line I will use a wye to split off for the Water Closet. Where is passes under the wall I will add a sanitation tee to a 2” vent just before the 3x4 toilets bend. Back at the wye I will reduce the continuing line to 2” add a couple bend 1/8 and 1/16 then where it passes under a wall use a sanitation tee for a 1.5” vent. After the vent use a wye to split the line for the tub and shower. Both tub and shower will have p trap of course.
Questions
1. Is there a better way to do this?
2. Do I need all 3 vents? I’m more interested in best practices over will it pass code.
3. Am I using proper size pipe?

 

[James Henry]

where exactly is the main drain line your tying into? draw it on your plan. is this a concrete slab floor?

 

[Sponsor]

 

[Jacob]

where exactly is the main drain line your tying into? draw it on your plan. is this a concrete slab floor?

I was afraid that is wasn’t very clean. I have added to the picture I hope that helps. Yes, this is under a concrete subfloor.
Additional question. The walls have all been opened up. Should I convert all the drains that are above the concrete slab to PVC or just leave the cast iron