Shouldn't be an issue, in the office at Securifi (at least when I worked there), there was a 24-port Gigabit switch that was fully populated and another switch hanging off of that, a NAS, a bunch of computers, a security system, various home automation gateways, about 40-50 wireless devices, and a bunch of other things, plus sensors and it didn't miss a beat.
Honestly, it sounds like you got a dud and there were a few of those, but not that many. If you'd contacted the support team, they would've swapped yours out for you and maybe they still will. Yes, the software had some stability issues too, but clearly if the hardware was as bad as you're saying, I think everyone on Kickstarter would've asked for a refund and I would personally not be using mine today.
Keep in mind that the SoC has a dedicated Wi-Fi offload processor so under normal Wi-Fi use, if you log in via SSH to the router and run the top command, you're only going to see 5-10% CPU usage. In your instance, it shouldn't be using more than maybe 50% with a bunch of things going on. The hardware is actually not bad, but sadly the software support from Cortina was less than stellar and Securifi got screwed over by them, as what they "sold" wasn't what was delivered.
I still have some software issues and I'm as eagerly waiting for a new firmware as everyone else here, so fingers crossed for this next release...