I think you'll struggle to break that into 2 areas - I'd use your stealth dresser for vegging, then this area for flowering. Remember that you're going to need to get in there to tend to your babies and you don't want it to be too much of a pain to do so.You might be ok with a 250w HPS in that space, but just ensure whatever you do you've got some good air circulation...
100% agree, exactly what I was gonna say. I learned this lesson the hard way, and my space is considerably taller (similar footprint/ceiling shape) AND I was only trying to get to one grow. You really want to keep accessibility a priority so your plants don't get neglected by laziness... imho.
On that note, if you do insist on getting both spaces into that one closet, your best bet would be two very narrow grow ops side by side, and not too deep to reach over to water everything.
Honestly, just having to hunch over or crawl to get in there would really diminish my growing enjoyment... I think your best bet is to maximize using as much of the closet as you can from the doorway... meaning work close to the door, not close to the back wall.
If you're going to use the whole footprint, I suppose you'll have no choice, in which case I recommend you design some rolling carts of some sort to make it easy to pull your plants back out of the crawl space to water... this is your best bet as far as accessibility is concerned in such a space. Especially if you want to make two spaces. Technically it might be possible to subdivide the space halfway back and make a cart that rolls out from behind a 'curtain' of panda film' that divides the two spaces... but personally, rather than try to ensure light isolation and good ventilaton in such an awkward arrangement, I would use the rolling cart idea and fill the whole closet for one setup, flowering.
Edit: Here's a pic of my rolling carts in a similarly 'long and narrow' eve closet:
Thanks to these new additions to my arsenal, I don't have to hunch under or raise my light to water... just roll the cart out for a minute, water up, and roll right back into place.