You are in predominantly ASUS users forum, so suggestions like the one above are expected. There is no "one size fits all" in WiFi world though, so based on your simple requirements I would suggest to you something different:
If you need good set-and-forget WiFi system, more than enough for your 250Mbps ISP line, go with Netgear Orbi RBK50 (good even for 400Mbps ISP). It is a bit expensive and not the latest and greatest, but proven reliable, very user friendly (10min setup), very fast (has designated WiFi channel between the router and the satellite), with excellent WiFi coverage (up to 5000sqf, ideal conditions though) and you can connect 7 wired devices to it (3 x LAN on the router, 4 x LAN on the satellite), if you need to. It will cover your house with a strong signal for sure, the family will be happy with your decision and you can focus on more important and pleasurable things in life than tweaking your WiFi router.
Avoid this particular ASUS RT-AC86U due to inconsistent build quality, high failure rate as a result and still unresolved software (or hardware) issues. There are hundreds of threads here on this forum discussing RT-AC86U issues. Don't install any custom software, if you don't need to. Scripts, USB sticks, swap files... if you just need fast and reliable WiFi connection, don't waste your time with flashing, resetting, long setup processes, fine tuning of hundreds of options, etc. Also, you don't need an AX router now. They are all for early adopters, very few AX devices are available and WIFI 6E (with 6GHz band support) is already around the corner. It is not going to be an investment in the future.