We have a T shaped pool with a large shallow leg (so we have the best of both worlds, I guess), but our deep end sounds a lot like what you are describing for your pool. Our deep side is 16x22, and slopes from about 3.5/4 ft to something like 7.5/8 bowl over a 22 ft long run. I'll attach a picture from when they were draining the pool last week to begin our renovation so you can see the slope. Not sure how it works with a vinyl pool or in a new construction, but our deep end is not quite as deep along the edges and drops in the middle. That may have been designed as the diving well for this pool and not a consideration for you.
As far as the slope, it is quite steep. No one can really stand on the sloping part comfortably. I am 5'4", so in about two steps off the top of the cliff and I am treading water and it doesn't matter if the deep end is 6 feet or 60 (consider that if you want to keep your head above water, the distance up from your shoulders up is something like a foot, so for me, after 4'4" depth I start getting to where I begin to tread water). My husband is 6' so he can go a little further before he is treading water. When we have parties, the adults tend to cling to the sides in the slope area with one hand on the coping, and one on their frosty beverage. The kids (5-10 yrs old) and the big kids (some of the 40 year old Peter Pans I work with, ha!) spend all their time cannonballing off the diving board (which is now gone, so that's over) and when they wear themselves out with that, they go to the shallow end which is between 3/3.5 feet deep. Or they try to use a lounger as a pirate ship and spend all their time trying to throw each other off of the raft.
For how you are describing using your pool, I'd recommend a bigger shallow end with a steeper drop off into the deeper end. Standing on the slope will be challenging, and when the pool is a rockin' with kids jumping around and stuff, it's difficult to stand still (and not spill your drink!) when you are buffeted by the waves without grabbing onto the coping. Since there is only so much space along the slope to stand and grab the wall, your friends are probably gonna want a little bit of personal space and not be crammed right up against you, so someone will have to be a foot or two further along up or down hill.
We are mostly float around people, too, and in a lounger it doesn't matter how deep it is, but on a noodle you do need some depth to float with. When I swim around (for simple exercise, but not with fancy underwater roll lap turns), I have no problem swimming in the 3.5 depth areas of the pool. My arms and legs don't hit the floor or anything. My wingspan is probably similar to my height, so I'd guess my arms are about 2.5 feet?
One thing I thought looking at your design was you might think about having the play ledge be the top step of the pool rather than the second. That's what we wanted to do to redo our steps but the budget ended up axing the idea entirely. A 6-8 inch deep play area seems perfect for your kids until they are out of toddlerhood and want to get into the open water to swim. It would be shallow enough to play toys on, sit and splash, etc, and will be really warm water because it's so shallow. On the 2nd step, if it is another 6-8" deep, think about how tall your kids are or how tall their torsos are, and if you think the play is more likely to be seated or standing for the majority of the time. We have a small swimout in our deep end that was about 8" deep and I love sitting there in the warmest water and thought it would be perfect for kids (if only it were bigger!)
