Although the processor is older, the assembly is done on-demand and is not older than some months, thus CPU paste shouldn't be an issue. We had no overheating reports or similar, yet. We have no first-hand experience with Suricata and/or zenarmor. Although zenarmor states 8GB should be enough for 100-250 devices within their documentation - still hard to extrapolate. But 3 users feel like this isn't too much load.