I think building it yourself works well for routers and NASes, but there's a gap for WiFi. Lot of the bells and whistles that make modern wifi perform well (beamforming, MIMO, ...) is locked behind proprietary software and your homemade access point will never work all that well.

Interestingly, this is also something MikroTik isn't very good at - their long-range wifi is nice, but their consumer wifi used to be stuck at 2x2 and basically worse than cheap Asus "wifi router" which is somewhat embarrassing.

For switches, if you want fast, for small installation it is hard to beat the Mikrotik 4xSFP+ 10G switch for $150.