I'll try it first in A18 and then revert to A17 if I want to play with more sleepers.
I've played "through it" now, meaning, I escaped the skyscraper. It took me roughly one day, and I spend the night mostly afk in a save spot. I found more ammo, eventually had 230 rounds left, and the (lvl 6) AK still had ~ 20% durability. But I also had found a stun baton and a sledge hammer. 'Twas amusing, but should need some further tweaking. Particularly should it not be possible to skip floors easily by jumping down, I must've skipped at least 5 floors that way. There is too much good loot (food, clothing, tools) and the AK seems overly strong, better give more ammo for a weaker weapon - you can 1 shot most zombies as long as you hit the head. The problem with sleeper "pockets" is noticable as well, when you can shoot down sleeping zombies through a door or window and their friends don't wake up because you are not in the same area with them.
Maybe instead of a gun, a melee weapon would be better, of course you'd still have to deal with the zombies on the roof - give a gun with ~ 50 - 80 rounds, after that, melee.
Anyways, I think it's a nice alternative start, already worth ~ 1 hour of gameplay, with a few tweaks, I bet you could squeeze at least another thirty minutes out of it, if you really wanted to and worked on the POI accordingly, probably much more. I guess you could just copypaste a whole bunch of additional floors in too.