Why not put the sun box behind the router? I think you can set up the sun box to do your NAT and firewalling. Although I think your Linksys router has a very limited firewall capability.

Personally I would run DHCP on the router. If you have your sun box in front of the router handing out addresses, you would have to push DHCP through the router, which i don't think you can do with the linksys (Im not positive about that one.)

You would need to enable port forwarding if you want anyone on the outside to access your servers on your internal network. Usually DNS is used in large networks, you can run DNS if you want, it isn't necessary, but its good if you want to play around with it.

In terms of services to shut-down to be more secure. Basically shut-down services that aren't needed (ie. sendmail, telnet, ftp, etc.....) if you need services like telnet for example, use SSH or SFTP instead of the the insecure FTP.

sorry if this seems scattered...just got into work and doing too many things at once.

hmmm...do I have my priorities straight?

anyways...hope i could help.