I have an APC metered PDU (AP8870) that gives me power, temp, and humidity stats for the rack

Windows Desktop OS is optimized for foreground applications, GUI’s, etc, whereas Server OS is optimized for background services, multiple user connections, and minimized need for downtime.

Neither of them are NAS software. Sure you can set up an SMB share on desktop, or build a fileserver in Server OS, but as youre wanting to replace a Network Attached Storage device, there are better options out there.

You could get a Supermicro server off eBay for cheap, either 2, 3 or 4U, and motherboard generation around X10 or X11. If youd rather a tower, then something like a Dell T440. Load it up with the drives you want and throw TrueNAS on the OS drives. TrueNAS is free and does a really good job of what it was designed for.

A - you need to make sure that the opposite side can be removed, or has sufficient venting. Rack equipment moves air front to back (cold aisle to hot aisle) If all you have for venting is the top then youre going to need some heavy duty fans to lift the hot air out of the cabinet and exhaust it somewhere

B - You can buy rack rails - theyre basically angle iron, and either tapped 10-32, 12-24, M6. AV racks typically use tapped rails. Server racks more commonly use square holes that accept cage nuts with M6 screws. Assuming you have 72" internal clearance in height, then https://www.server-rack-online.com/7205-es2p.html or https://www.penn-elcom.com/us/42u-rack-strip-with-square-holes-1-16in-thick-r0863-2mm-42 rail kit is what youd want (the first link is for a pair, vs the second link is per rail). Dont forget the cage nuts and screws https://www.server-rack-online.com/hdw-105-50.html

For 19" racks, the distance between hole centers on the rails needs to be 18 & 5/16 inches. If you dont have about 20 inches between the cabinet walls (assuming about another 1.5 inches taken up by the width of the rails) then this cabinet is probably a bit of a lost cause

All that said, for the $100 you’d spend on rails, theres probably someone out there with a proper server rack trying to get rid of it for that or less

Visio has been pretty much standard in all my work roles for rack elevation and network diagram drawings, so I use it for home stuff too

If self hosting, I’d virtualize the workstations and utilize GPUs designed for virtualized engineering workstations, like a Nvidia A100

As for access, you could go through the trouble and expense of exposing something like VMware Horizon VDI to the internet through a reverse proxy if using virtualized workstations.

A better option would be to go with Cloudflare Zero Trust. You run a small agent on your side, and people outside needing access sign in through Cloudflare, and you can grant very specific access to what they need. It’s kind of like a VPN but with much greater control over where someone can go while connected

You’ll want to segment the workstations off into their own VLAN, and you should be using a good firewall on its own hardware to lock down access between outside and the workstation VLAN (ie only allow connection from Cloudflare service endpoint urls to IP range of your workstations)

APC Symmetra LX 16kVa wired to a secondary panel. That panel feeds both the rack and computer receptacles in my office.

For extended outages I have a natural gas powered permanently installed backup generator. Generator start and transfer switch is fully automatic

As far as the rack and my office machines are concerned the power never goes out, even though my area experiences frequent brownouts and winter has a pretty good chance of seeing an extended blackout

Paessler PRTG is among my favorites outside of LogicMonitor, and has a freeware version https://www.paessler.com/howto-free-network-monitoring

I’d also look into Nagios Core, Prometheus, Zabbix, and Zenoss - All capable monitoring solutions, just dig into to see what it can do and if the feature set and layout works for you