The issue of WIFI users being unable to connect while WLAN users on the guest network can access all resources indicates a problem with channel overlap or interference. By reconfiguring the channels, interference can be minimized, improving connectivity for WIFI users. According to the table, AP 1 and AP 2 are using adjacent channels (2 and 1), which can cause interference. AP 3 and AP 4 are using non-overlapping channels (5 and 11), but they have very high RSSI values (-44dBm and -41dBm), which can also cause interference. A possible solution is to use only non-overlapping channels (such as 1, 6, and 11) and adjust the power levels to avoid excessive signal strength. References: Wireless Troubleshooting - N10-008 CompTIA Network+ :
5.4, Network Troubleshooting Methodology - N10-008 CompTIA Network+ : 5.1

BGP stands for Border Gateway Protocol and it is used to exchange routing information between autonomous systems (AS) on the Internet. A perimeter router is a router that connects an AS to another AS or to the Internet. Therefore, BGP is the best suited routing protocol for a perimeter router.
References: Network+ Study Guide Objective 2.4: Compare and contrast the characteristics of network topologies, types and technologies.