I have an older APU1C4 with two WLAN cards (WLE200NX) and it's hosting two physical APs and a few virtual ones (diff BSSID/subnet one running at 2.4 ghz other at 5). I just run vanilla Debian on it... The SD card has finally become corrupted over the years, however. When I reboot it, all my changes that were supposedly flushed to disk are lost. Thankfully I only reboot it occasionally when there are critical kernel updates. I just rsync over the filesystem in memory to facilitate restoring the previous configurations.

Anyway, I run various services on it, aside from hostapd... It acts as my firewall, gateway, access point, and runs some other services like nginx to proxy some services from my LAN across subnets (like plex, etc) and motiond as a security camera monitor. I've used it as an SSH style VPN at times, in a pinch. When our WAN goes down I can simply plug my phone in to the APU via USB and tweak some iptables rules to use the LTE connection from the phone over USB network interface.

I also have a newer APU2C4, along w/ an AC WLAN card and an msata drive... have had it for years just sitting there, grr. I really only got the newer one since it has AES-NI support on the processor and I can do much heavier VPN traffic, but the SD card issues have become annoying, so I think this post has encouraged me to finally set it up this weekend... Thanks :P

Anyway, I wouldn't hesitate to pull the trigger on any of the pcengines stuff... Go for it!

Just make sure the WLAN cards you use are well supported via hostapd. :)