Not sure why this doesn't exist. I don't need 12TB of storage. When I had a Google account I never even crossed 15GB. 1TB should be plenty for myself and my family. I want to use NVMe since it is quieter and smaller. 2230 drives would be ideal. But I want 1 boot drive and 2 x storage drives in RAID. I guess I could potentially just have 2xNVMe and have the boot partition in RAID also? Bonus points if I can use it as a wireless router also.
All of those HP minis have 2 NVMe slots. If you're looking for more bays maybe a QNAP TBS-h574TX (Core i3-1320PE) will bit your needs better. Or the Asustor Flashstor 6 FS6706T.
But I want 1 boot drive and 2 x storage drives in RAID
One other possible approach to this is to go with the 800 G4 or the 800 G6 as they also SATA port you can use for your boot drive.
You can also boot from a fast USB 3 flash drive, since it's your boot drive it won't be as bad as you think. Consider some servers boot from SD Cards and other low performance media with almost static images.
I work with real servers. SD card boot media is generally a bad idea. VMware officially semi-deprecated it a while back. Unless you tune your install to redirect typical I/O to the durable drives (which is going to be a pain, having to find and reconfigure all those services), typical logging to disk and various temp files are going to wear it out pretty quickly.
I would just use two drives and not separate the OS. That way, you also don't have to worry about the OS drive failing and taking down the server.
Just be careful if you reinstall. I'd suggest deleting the OS partitions first, then reinstalling to the empty space, instead of trusting the installer to do it properly.
Unless you tune your install to redirect typical I/O to the durable drives (which is going to be a pain, having to find and reconfigure all those services), typical logging to disk and various temp files are going to wear it out pretty quickly.
I think you'll be out of luck for 3 slots, but you could always use the native slot for OS and dock the other 2 via USB with RAID capability in something like this.
For minipcs, have a look at aliexpress. They tend to have the branded options much cheaper than amazon. Trigkey, minisforum, Beelink, etc.
The OP would be better serve with a second hand mini computer from HP or Dell than that crap. AliExpress brands (including Minisforum) are all fun an games until you run into some UEFI bug that will never get a fix and won't you boot some system or have some feature, or your board doesn't have proper ESD protection and randomly fries when a USB device is inserted.
I run a trigkey (AMD 5700u) as my NAS (unraid) and homelab, and a CW p-5 (N305) as my router (opnsense), and have no problems at all. So they for sure boot Linux and FreeBSD, which is 90% the case.
Unlike some old second hand, new hardware is more powerful and energy efficient.