I’m currently in the process of building DAS server. Inspired by 20 Bay L4500 DAS w/ Linked PSUs
I have EVGA SuperNOVA 750 G2 PSU and 24 Seagate Constellation ES.3 SAS drives (idle 6.75W R/W 11.27W). Is this PSU going to be enough?
Yes, that PSU should be plenty.
I would recommend that you not put more than 6 hard drives per set of wires coming from the PSU, though.
Silly question. Since I don’t have a motherboard in my DAS design,
can I use PSU 18pin connector as an additional sata lane?
No, but you can use molex connectors with adapters, such as these: