Networks

I think my original threads fallen out of view so i'll post the new questions here..

So i have 3 sites connected via leased lines in a triangle configuration.

Each site will have a windows domain controller with active directory updating via master/master replication between the different locations.

A few things have me confused.. Does there need to be more than 1 domain server at each location (in case of failure) or will authentication automaitcally locate the other ones?

Router configuration and DHCP has me also.. Should their be two routers at each site, each handling a different leased line?

I am guessing each router should be connected together via a fiber channel for speed and each router should be connected to a core switch?

What i dont understand is what controls DHCP.. Does there need to be a DNS server at each site?

Further down the a standard wired network setup seem to change to a star topology. Does this not introduce a single points of failure?

Final question (i know i know), each site required an internet connection. One site has to have a web server. Should each site then have an internet connection to reduce traffic between locations?