Don't get locked into having the clean out at the bottom. If you need to have fittings lower, I would remove the CO and put it higher it that's what it takes to put the other fittings in at the proper height.
If the heights work out, then leave the CO there.
You lav will need a vent and so will the washer utility drain.
Those vents can tie back together at 42" but can't tie back into a waste stack.
You will need to run a separate vent to the next floor, or use an AAV, which can have it's own problems.
An AAV needs to remain exposed and have available air for it to work.
There also needs to be a primary vent in the system for it to work, they are secondary vents.