Untangle initial set up of external/internal interfaces when using asus router in access point mode

need help in setting up untangle for home use ( using my on firewall appliance). i have an asus router which i will be using as an access point. my questions are as follows (my isp provides dynamic ip address):

  1. in the external wan interface do i select auto dchp?

  2. or do i select static? if i use static what ip address do i use. i will assign the asus access point and ip address of with subnet mask but what gateway ip do i use?

  3. in the internal interface what configurations i will use here. not sure as i am confuse about the ip address, how to select them , etc.?

trying to learn untangle as a beginner. any step by step instruction for above set up will be highly appreciated

thank you