If you don't know, use the default (auto layout). There are too many things involved to give you a size for everything.
Swap should be twice the size of memory (rule of thumb)
If you are using it as a workstation - default is fine
If you are adding applications such as mailserver, ftp server, web server....each requires different things. Let's say you are setting up a mailserver using Sendmail. Your /var/spool/mqueue should be it's own partition so if you start getting hit hard with spam it won't fill your /var or / partition. Same type of scenerio with ftp (just a different directory).
Solaris should give you minimum and/or recommended sizes of the partitions but it doesn't know what you are using it for either.