I'm sure I haven't maxed the connections, I've had many more devices connected at times. The Asus RT-AC66U is a fairly high performance router, and should easily handle 40-50 connections without breaking a sweat.
The ASUS RT-AC66U is a 5th gen dual-band Wi-Fi router, and the launch platform for the new ASUS AiCloud service. Its speed reaches 1.75Gbps, utilizing the Broadcom 802.11ac Wi-Fi controller and working in 2.4GHz and 5GHz. The 5GHz band supports up to 1.3Gbps, exceeding current Gigabit wired transmission and 3X faster than 802.11n. The RT-AC66U offers smooth lag-resistant multitasking and super-fast streaming, while ASUS AiRadar intelligently strengthens wireless connections via powerful amplification, offering future-proof optimized performance.
As far as avoiding WPS, that's not possible with the Lionel LCS WiFi unit if you want to connect to a network and not run in Access Point mode. From the manual, the only way to connect to the network...
If your Wireless Router supports “WPS” (WiFi Protected Setup), then you may add LCS WiFi to your home network. Now your iPad (or other device) can seamlessly access the internet and run your layout. However, if your home network is busy, you may experience latency (slower response to your commands) when using the JOIN to NETWORK mode of operation.
