I don't think what you want is possible in a single chassis.
One of the only half depth chassis i can think of is the Sliger CX3701. (by half depth i am assuming you mean 15" or shorter"
It's 3u, can fit a mITX motherboard only and has 10 bays of storage. Every mITX mobo i can find only has one pcie slot.
But even then i don't think you can find an elegant way to get enough sata ports with a mITX mobo to 10 internal drives and 14 more external drives even with hbas since i don't think broadcom makes a 16e8i hba.
The only way i can think of is getting a 24 internal hba and have 14 go outside the case and 8 stay inside and use 2 mobo sata.
things do change a little bit if you have space for 18" depth. The Sliger CX3702 can support mATX mobo and some of those do have multiple pcie slots letting you use 2 different hba cards.
That said i still can't think of any external enclosures that'll fit the extra drives.
Without depth as a factor, so used super micro stuff might work for you?
TLDR: i can't think of any good options for half depth.