You probably need a dedicated sysadmin as soon as you've got physical infrastructure that needs to stay online for your business to keep running - you honestly

You probably need a dedicated sysadmin as soon as you've got physical infrastructure that needs to stay online for your business to keep running - you honestly probably need this even if you're leasing dedicated hardware. I used to work for a company that leased dedicated servers, and I talked to A LOT of customers that lost their business or lost a significant amount of their runway/savings/whatever due to mistakes caused by not having a real sysadmin around to handle their infrastructure. Long running issues they didn't have the experience to troubleshot, bad (or nonexistent!) backups or restoration procedures, extended outages due to server related issues, bad update/firewall/other security practices, etc. There's pitfalls with every option, but running your own infrastructure is a completely different skillset from developing an application, and is a professional trade in and of itself - you can try to force this on a developer and hope they have the time and expertise to handle all of these different things and run the risk that they don't, or you can tack on another ~100k/yr for a professional. And as you grow, so does the complexity, and maybe now your infrastructure spans a lot of racks, and you need network engineers, you need multiple sysadmins, etc, etc, etc. You can't DevOps your way out of managing physical infrastructure