JohnOregan,
I am also new, but by several weeks, maybe 5 or 6 and I have lived in the entity files alot recently, so I will offer my little experience, though some of the more experienced people may know better than i.
For adding weapons, as i wanted to do also, to add beam weapons to some of the advent craft that used projectiles, create a folder in the mod folder of your stardock game, if you don't know the folder path, when you open the game and go to options one of the options will be to show mod path, do that and it will create the set of folders you need at the folder path area. It is like c"\users\name\appdata\local\ironclad games\sins of a solar empire\mods
I reccommend creating a shortcut to this area and putting it in your quicklaunch folder for quick access, or on the desktop, or whatever you want to get to it quickly without having to go to my computer... and through all the folders to reach it.
Anyway, once that is done, download the forge tools from the Sins website, and unzip them, usually on the desktop or my documents folder, but whereever you want them is fine. after extracting them copy the game info folder to the mods folder to a folder you want for your updated weapons mod, call it my mod, or John's SuperWeapon Mod, or TecWeaponMod, or whatever you want and once copied, open the gameinfo folder. I suggest right now to highlight all the included files and to select properties from the file menu and set all of them so that read only is now unchecked. It will make accessing and changing the files and closing them easier.
Open Two craft files, like say the tec scout and the tec capital battleship for example. TechScout will be under FrigateTechScout.entity and the batteship under CapitaShipTechBattleship.entity, you will get used to finding these and some changes you make now may be easy, but others you want have ideas about and try yourself, may not work quite so readily, but that is okay, you can always ask questions and there are lots of experienced people in the mod forum and some have already done what you may want to try. Others you may have unique ideas about and may have to experiment with, but so far I have been able to get help with every idea i had and it worked well with all the help.
Anyway, inside those two files go to the capitalship entry where you will find something like:
now open two files, one for the craft you want to add the weapon to, the other for the craft that already has the weapon you want. If you want to make a copy of this file it might be a good idea, or not as we can re-copy over the whole gameinfo folder again clean if necessary. Anyway highlight the weapon you want. Something like numweapons 1
weapon... all the way down to where it ways weapon again, or it says mweaponindexForRange 0, highlight and click copy and then go to the other file, usually the frigate file where the weapon you want to change is. Also there will be craft that have no weapons. The carrier is usually one of them, that you may want to add weapons to, so you can use this to do the same for that file even though it has no weapons. The wonderful part of may of these files is that they follow a pattern so even ships with no weapons will ususally have a numweapons line with 0 on the end. It makes it easier to change values and try new and cool things.
Anyway, copy over the numweapons line from the capitalship (or whatever ship you have that you want the weapon from) to the file where you want it, (in this case the frigate file. So my projectile lines are replaced with the beam lines. now save the file and when you load the game go to the options menu and find your SuperWeaponsMod folder, or whatever you named it and select it and then click enable mod. if things are nice, then you will get the music and a new screen in a minute or so. If there are entries that have been changed that the program cant interpret or understand (once i changed too many values and apparently some were out of the value range to be understood) then the game will freeze attempting to load the mod. simply hit control alt delete and open the taskmanager and end the game, and then go edit the files or replace them with clean versions from the forge tools copy and try your changes again. You may want to do only small changes and save and see if everything is ok, or only one of say 6 or 7 changes and see which one keeps the game from loading properly. Anyway, when that happens ask someone in the forum, or try another tactic. You can probably get it to work with some help. 
Happy Modding and take care,
Sincerely a fellow beginning modder,
-Teal
