There are ways to figure out what triggers the reboots on the Asus router by looking through the log.. It may not be the hardware, rather dependent on the firmware and settings. I've used one for a couple of years now and it's been rock-solid, haven't experienced a single reboot. The web interface had locked once, but SSH to it still worked and internet/WiFi was fine.
As to your questions, if the Ubiquiti AP works for you, just keep using that for wireless. If you'd like ease of use, just get any decent router with gigabit ports and good brand name, and turn off the wireless on it. Recent variants have faster hardware, which comes into play with higher bandwidth and firewall/QoS settings load, it can stress the CPU/memory. Asus/Netgear are my personal preference, with D-Link/Linksys as a second choice. This option gives you some flexibility, as you can still use the Wireless on the router sometime in the future if you decide, for better coverage, guest wifi, or to distribute the wireless load between clients.
If, otoh you have the time and will to customize a pfsense box and learn to use it, by all means, it is a great system. The appliances they sell will most likely run over your budget though, so you'd have to custom build and install everything. A thin-client / mini-pc may work well if the hardware is compatible, and you already have a switch (hopefully gigabit).