1) you mean the script has to bring up eth0 ?
if so, you can call "/etc/rc.d/rc.inet1 eth0_start "
and "/etc/rc.d/rc.inet1 eth0_stop " to close the connection.
maybe after starting up, ping the server swaret needs to check the connection.
2)if you use a 2.6.13 kernel there is the possibility to set a max kb/sec for a certain ip
by using iptables-rules.
i don't know the ins and outs, but it's there.
3)just type the commands in the script.
4) i really wouldn't run swaret or any autopackage-manager through a cronjob.
( i myself never use them )
if you just update without at least taking a quick look at the changelog,
some things might brake.
it's a bad idea...