First off, let me say that this is an impressive mod. I highly encourage you stick with it. I know I'll be follow its continued development.
I would say setting up an actual issue tracking system somewhere even if you don't open source the code (GitHub or any place like that would work). Being able to track issues when more and more people start using your mod will save your sanity in the long run.
A couple of issues from me (I'm running FML: MCP v9.05 FML v22.214.171.1240 Minecraft Forge 10.13.0.1180 37 mods loaded, 37 mods active with Shadow World 1.2.1):
The shadowworld.cfg is empty (as in zero bytes). This might be just a side-effect of the mod being in alpha but I thought I'd point it out anyway.
There are a couple of ID conflicts with The Mist of RioV mod. One for an Enchantment with an ID of 82 and another with an Entity with an ID of 8225. Trying to configure these IDs for Shadow World lead me to discover #1.
Use NEI to view the normal recipes. They are mostly like vanilla, so you can make Shadow Stone Bricks out of four Shadow Stone and so on. If you want to know how to craft the Swords+ you have to figure it out yourself...
Very nice mod here. I would suggest going over what can be found in the shadow dimension in the original post. You don't have to tell people everything but telling them about the items and what they are used for would be good. Besides what I saw in a mod showcase, I didn't see many above ground structures. That might be something to work on to "fill the world" a bit. I think a small tower designed to look like some one was trying to harvest the shadows as a weapon would be something.
Hehehe... You think you're the master of all Shadows, eh, Zed? All I see is a puny little shade hiding in his armor... Run, little shade, before the true darkness consumes you. Your weapons you so covet can't protect you...