The answer to your first question is it depends on what you want you Linux box to do. I'm sure that everyone has their own answers to this question. I am still figuring it out for myself but if I'm doing a generic install (not for a database, or a specific application) I tend to go very basic:
100 M /boot
1500 M /var (log files go here and can get out of control if it fills up it won't kill your system) If this is going to be a webserver with a bunch of content make this bigger or create a /var/www partition.
2 time RAM for swap
the rest I usually leave /
If users are actually logging into the box (not just using services) I will allocate a few gig to /home (again if it fills up it won't kill the system)
I usually leave a couple gig un-formatted in case i need to put it somewhere.
Table 3-2 at http://www.tldp.org/LDP/intro-linux/...ect_03_01.html
shows each of the file systems and defines what goes in each. Maybe it will make it a bit clearer.
/etc/sysconfig/network-scripts/ifcfg-eth1 is teh config file for a second nic.
It shouuld look something like this for static:
If Linux is not seeing your nic, I have not had much luck fixing that. I usually just put in a nic RHEL knows about. I'm sure there is a way, I'm just not quite to the level to give advice on it.
I've never setup e-mail, so I can't help.