Ryzen 7 5700G will easily handle Blue Iris.

Is the need for Intel QuickSync still a thing these days, now that Blue Iris works with substreams?

An AMD 4500u-based machine I look after consumes 15 watts (not a typo!) from the wall while recording seven 3.9-megapixel cameras. It is a mini desktop PC with a laptop-class CPU. CPU usage is about 8%.

Another system I monitor has a Ryzen 5 2400G with 19 cameras, most of them 3.9 megapixels. It is at 12% CPU usage but also has four virtual machines running (the virtual machines are likely idling right now).

Blue Iris doesn't need much memory. The 2400G system mentioned above has 4GB left over for Blue Iris with the virtual machines running.

I like to run multiple data drives, with each drive recording a specific group of the cameras. I format them with large 2MB clusters to significantly reduce fragmentation. I no longer use the "cascading" storage method, where your video files move from one drive to the next as they age. Avoid hard drives that use SMR recording technology.

There are many posts here along the same line. And, helpful replies.
Search is your friend.

Morning.
Have you made decision on this project?
Video security is not something to skimp on considering the recent injury which occurred in your Ghouse.
Adding GPU to a machine with plenty of resources does not have to break the bank. many great ideas throughout threads on this site however we forget about used or refurbed machines available out there.
There are many, for example, Dell T5810/5820 workstations loaded with DDR 32GB and up, E5-1620/1630v4 Xeon processors, AMD FirePro W5100 W7100 WX7100 GPU on board. the T5820 has a flex bay to accommodate NVME, T5810 NVME adaptors also available however not needed although we use them in large system applications. a simple SSD for boot and BI5 with additional 1TB WD blue for temp storage will be great. these machines can be found on EBay from reliable sellers even authorized refurb folks for under $500.00. you would need to add the 2nd drive.
Synology DS1821+ 8 bay NAS use any HDD. we use WD purple generally but for smaller projects or for cost savings we have clients purchase used Purple drives or they pick their own. liability of this isn't bad when things are in writing.

NEVER skimp on the switch. I would never use Netgear Linksys Etc. you can pick up a used Aruba JL684A 370w 24pt. though it is L2 and considered light L3 there's not much config to do if you do not understand networking/ routing. give it an IP address and run it. you can pick one up for under $600.00

Never skimp on cabling patch panels or patch cables though you don't have to purchase the most expensive, either. shielded cabling is best bet period. we have proven it over the decades via Fluke DTX and Versiv. though video quality speaks for itself when cabling is done right.

You mentioned 5-8Mp cams. Hikvision 2CD2385G1-I 2.8mm 4K Outdoor Darkfighter will push full 8mp if power and comm is plentiful. this model can be installed with or without its "conduit" or splice box. part # can be found on Hikvision USA. $136.00 on EBay and can be found on Amazon if you dig.

there is an OEM non labeled version of this camera on EBay and Amazon for $119.00 https://www.amazon.com/gp/product/B082H ... =UTF8&th=1
Just installed 25 of this with conduit mounting boxes outdoors, some in all day direct sun though it's not summer temps they rock. we can crank them up and watch the streams, network usage, bits bytes and all details with our tools. they have been flawless for 3 weeks now.

Granted it is humid and can become warm in Ghouses we have installed the Hikvision version in many Ghouses. have been in service since this cam was available, still flawless.

We do consider the cameras calling home or may try to so we put the cams on their own network. add additional NIC in the server and no issues. don't skimp on the NIC cost but doesn't have to be top of the line either. We use single 4 port secondary NIC and team them to have steady bandwidth.

Router also is consideration for performance, off-shelf consumer grade no bueno. Pick up a Cisco ISR or ASA at minimum. Hire someone to config for you. we do provide all of the above items, pre-configured and available remote support. If you're running out of $ at this point I suggest TpLink https://www.amazon.com/gp/product/B087Q ... UTF8&psc=1
This product has multi-core main processor and a secondary processor as well with 2gb memory. its throughput is amazing. this is a cheap router, not commercial but it smokes any of the Nighthawk routers. we know this because we have all of the commercial network testing goodies and can watch the action.

All in all

Dell T5810 with W5100 E51620v4 256GB SSD with win10 pro we can get for $500.00 or less with warranty. our cost mind you
4 port NIC, up to $125.00
Aruba JL684AABA $400.00
Hik cams mentioned above 16 x $136.00 -$2176.00
BI 5 $60.00 + -

Just my typical small project experience.
Best of luck to you

Thanks for the advise and feedback.
We shelved the AMD CPU and board for another time and purchased an i7-12700K, ASRock Z690 Extreme WiFi 6E, 64G DDR, 24port 400Watt POE, a case, cooling and other accessories. Hikvision seems to have a good reputation so we will probably go with recommended cameras like the Hikvision 2CD2385G1-I 2.8mm 4K .

The reason we are all over the place on this project is that I'm retired, but have greenhouses that were used in a nursery business. This project was started to assist a family member, a neighbor, and an acquaintance. Then along came Covid19 and the need for outdoor activities caused this thing to blow up. There were 3 and now there are 12 + a couple of volunteers. If things go back to normal, what we are doing will be overkill.

If we ever do expand into growing cannabis we will purchase another separate system and likely have it professionally installed. I and others were thinking medical grade CBD, but as was brought up, it could be mistaken for recreational cannabis and put people in danger. It could also cause some our supporters to reconsider.

Again Thank you for all the feedback.