The shower & WC connections are fine however your drawing shows the vent connected to the shower line by means of a Sani-tee. Tee's are prohibited on horizontal lines. You must use a Wye & 1/8bend or Combo

Thanks! So there is no problem combining the drain lines of the shower and the toilet? The distance between the two drains will be a little over 7'.

I should post that I'm in Illinois.

In your configuration the critical distance is from the shower trap weir to the vent opening.

The trap weir is the exact point on the discharge side of a trap where the standing water in the trap will spill out into the drain line whenever additional water enters the trap. (The word "Weir" means spillway, such as the spillway of a dam is properly called the damn weir).

Code requires a shower to have a 2" trap & drain-

Under the Illinois Plumbing Code secton 890 table I- a 2" fixture arm may be a maximum of 4' from the trap weir to the vent opening. The remaining 2" on the downstream side of the vent is classified as a "Vented Branch" and it may run an unlimited length.

The section of 2" from the vent opening to the watercloset is technically defined as a "Combined Waste & Vent", meaning that it not only provides the drainage from the shower, it serves as the vent for the WC, so you are fine as long as the shower P-trap is not more than 4" upstream of the vent. If your shower is large and you cannot achieve the 4' keep in mind that the drain opening in the shower does not have to be exactly in the center. You can place the drain anywhere within the shower providing you slope the shower pan at not less than 1/4" per foot or more than 1/2" per foot towards the drain.

Thanks for the detailed response. I now have another question just so I know I'm clear. Your last paragraph states that the p-trap of the shower can not be more than 4' (I'm assuming you mis-typed 4") from the WC drain. My bathroom layout will make this quite tough, but as you can see in my drawing that I am planning on give the WC it's own vent line on the other side (left side of the drain). My combined waste & vent line is actually a redundant vent for the WC.

At the end of the day, I'm wondering if it would be a better idea to use a wye to tie the shower drain into the WC drain. I would tie in after the closet bend. The last thing I would want is waste material to creep it's way up towards the shower via a combined drain line. That would be next to impossible with a wye.