If all those IP in the same subnet, you can only use one ethernet card.
If it’s /32 IP, as it’s in different subnet, you can use 3 cards, or you can also use 1 card.
About load balance all of your connection, you can see on MT wiki, using conn-track, nth, and src-nat each conn-track to each public IP.
I have situation like Yours, But If your Public IP address have the same Gateway ar if thay are from the same ISP , thay get the same Gateway IP and beacoue of this like me We are Stuck into ONE.
you can not use it like 1x772
even if you make perfect balansing you will have single tcp connection up to the max speed of 386 ..
allso if you make roundrobing (one connection to adsl1, next to adsl2,nexto to adsl1,…) you will have some MSN problems .. allso https may have problems etc
You maybe want to have ftp, http, mail, etc .. to be routed at adsl2 all the rest to the adsl1 .. so you will be able to play some online game while
some one else is downloading HTTP
For testing purposes i did activate 4xadsl .. it was funny to have it all work …