Start with the building, not the access point. Thick walls, plant rooms, metal racking and stair cores affect WiFi more than marketing specifications do.
Do not rely on one powerful access point in the corner. Several lower powered access points, placed sensibly, usually give better roaming and fewer dead zones.
Separate guest traffic from business devices. A guest SSID should normally sit on its own VLAN with firewall rules that prevent access to internal systems.
Document SSIDs, VLANs, switch ports, IP ranges and admin access. Future you will appreciate it. Future you is usually tired and slightly irritated.
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