Thx for links! I feel stupid for not looking them up in google first
The Keybind link worked, however the Gui_Overlay showed some errors. I believe I took care of them (i.e. @Init annotations) however the bindTextures method did not like using a String for its location:
It is an older tutorial, though most of the information is still very useful. Minecraft uses ResourceLocations now:
private static final ResourceLocation texture = new ResourceLocation("yourmodid", "textures/gui/yourtexture.png");
mc.getTextureManager().bindTexture(texture); <-- bind a ResourceLocation
As for the PotionEffects, that's just part of the example, but you don't need to use them in your overlay. If you do want to use them, you should google 'Java generics' and look in the Minecraft code for where they do the same thing, I believe it's in the Inventory Gui that you can see active potion effects.