You could use MCPC+ (google it) but galacticraft is extremely buggy and causes a lot of crashes when you use that, but its the only way to install plugins at the moment
use bukkitkitforge.com, assuming you know how to make a MCFORGE server, just put it in the mods folder, and then you can load plugins, but BTW, essentials pre-release is out, but it has so many bugs, Its like a ant hill
When BukkitForge is officially released for 1.5.1, you should use that.
Put it in the coremods folder, start and stop your server once, and then use your server like a normal Bukkit server (put plugins in the /plugins folder etc).
For now you can use MCPC+, although I myself have no experience with that and Galacticraft.