If I understand correctly you want to connect to a public hot spot. So, for details you should ask the operators of that hot spot, but this is some genenral information which possibly apply:
1: You don't change the MAC address on your Amiga, but you probably have to tell your MAC to the operators and they'll allow your NIC to connect to their access point.
2: They will probably give you a password which you will have to enter on a web page running on their router. After successful authentication, you will get access to the internet.
3: Dunno, but I suppose DHCP will be required indeed to use the hot spot.
4: See JJs answer (I guess)
