Yup. I'd go for it.
I picked up a 3040 SFF with a 500GB hard drive about 8 months ago for $368 from the Dell Outlet. Also i7-6700 and 8GB ram. So pretty much the same machine but 3 year warranty. I would have prefered the SSD though.
Should be plenty of machine but load will be determined not just by the number of cameras, but data rates, frame rates, resolution.
I run 11 cams mix of 2 and 3 MP at 10fps. BI reports totals 255 MP/s and 4600 kB/s. CPU sits between 15 - 18% for reference.