Cleanout for WC run

My main question is about the Powder WC line in that I was unable to use a 45* wye and therefore do not have an obvious way to add a CO to this run... do I even NEED a CO on this run? Please see the attached pictures. Drains are black, vents are white. This is fairly accurate depiction of the overall system I'm planning & implementing (all new), though not to scale (floor heights and major horizontal run lengths not accurate).

I am thinking of adding a 2-way CO as indicated in the pictures. Please advise... (also if I go this route do I need to use an actual 2-way CO fixture or could I use a Test-T here?) NOTE: the WC uses a 4x3 closet bend to stay within 2x8 floor joists. In order to stay in the ceiling and get around the chiimney there's a series of fittings at 'odd angles' so I do not think I can use a WYE w/ CO on this run.

If you see anything amiss anywhere please point it out to me. (The master has a false wall behind the WC allowing the diagonal run of Lav behind that wall and out of view.)

Thanks in advance.

You're not required to have a cleanout on the upper floors for the toilet.
The chances of that 3" line clogging are slim to none.

The cleanout should be just before the pipe enters the concrete floor to go underground. It should be a "test tee" so that if it EVER did plug up overhead the snake could be sent to the downstream side to unstop it. IF you ever have to remove the plug from an overhead line, because the line is plugged, you would appreciate NOT having to do it.

Seattle does require a cleanout at the base of the stack.

The Powder room is on the main (1st) floor. The cleanout I was asking about would be at the basement ceiling level. Does that change any of the replies?

There is a cleanout at the base of the stack, but it is a Wye leading down towards the sewer. The stack base is the original 1910 era (presumably). I am merely connecting to that original stack base.

NOt really. A cleanout at the ceiling would be the LAST resort if the line were clogged.