First of all, use LVM, dont use classical file systems. This way you can increase the file system without any issue.
So you will need a VG, and lets call it rootvg, in which you will find the LV's which you system will have
first: /boot cant be in the "rootvg" as Linux doesnt support this, cant boot from an VG, so this needs to be separate from the VG.
/boot: 80MB (ex. /dev/sda2)
/usr: 5-10GB (ex. usr_lv)
/home: 75GB (ex. home_lv)
/tmp: 512M and up (ex. tmp_lv, if in case you need bigger you can increase it real time, so you dont need more at the begining more then 512M)
/var: 2GB (ex. var_lv)
/var/log: 2GB (ex. var_log_lv)
/opt: 1GB (ex. opt_lv, can be increase real time, so no stress)
swap: 4Gb x 2 = 8GB (ex. swap_lv)
Have to keep in mind that all the file system can be increased real time, so you dont need more at the start, also some additional "free pv's" in your VG is good, as you can increase some of the file system which may need.