You are using 2 NICs with the server doing routing, providing DHCP internally and proxy to the internet connection. Excellent! You added an access point but it doesn’t do DHCP. And the USERS (in this case visitors & guests) want Internet. You were not exactly clear who the WAP was for. You have three choices –
1st setup a small Linux box with three NICs between the server and the internet. NIC 1 to the internet, NIC 2 to the server thru firewall, NIC 3 to the WAP with DHCP service for private addresses. This put the WAP and your visitors in the DMZ (DeMilitarized Zone) outside your network but with Internet access. 2nd setup a system inside the network as ‘Internet Cafe’ and put the WAP on that machine (once again requires two NICs). 3rd and least expensive – Upgrade the WAP to a proper router/switch with DHCP service. Good luck.