@Wolf666:
Let's do it simple.
Taken into account you have a working pfsense WAN IP, got via DHCP.
Set:
1 - pfSense (LAN) IP 192.168.1.1/24 - set DHCP server scope 192.168.1.100 - 192.168.1.150 (if you need DCHP)
2 - Linksys IP 192.168.1.2/255.255.255.0 (disable NAT and DHCP server), set default gateway 192.168.1.1.
3 - Connect pfSense LAN to any LAN port of Linksys, also linksys WAN port should work if AP mode is supported.
4 - Connect the Switch (if you need) to a spare Linksys' LAN port.
Now any wired, wireless client should receive an IP from pfSense DHCP or, in case you are using static mappings, use their own IP (set them between 192.168.1.3-99 and 192.168.1.151-254, outside DHCP scope).
ALL your LAN is inside 192.168.1.0/24.
Check your outbound nat, check firewall rules.
Let us know if this simple configuration works.
Thank you so much Wolf666! It worked! I did what you suggested and turned on the enabled Dynamic Router RIP, then after that I switched my WAN intel nic to LAN, and LAN tp-link nic to WAN, then it worked! I saw some lights on the tp link nic was not blinking (there are 3 blinking lights, only 1 is blinking) so I tried to switch it to WAN. Then it worked! Thank you wolf666! I'll study this to learn more about pfsense. :)