AirostheTiger

Yep.

That depends on what, exactly, you want to accomplish. You can use Gimp or Photoshop, (if you use Gimp, make sure you install the DDS plugin), open up the texture for the skin you wish to add a tattoo to, (i.e. Data\textures\actors\character\male\malebody_1.dds and malehead.dds for males, Data\textures\actors\character\female\femalebody_1.dds and femalehead.dds for females), then copy/paste your tattoo image onto the texture. You should note that every non-beast race female uses the femalebody_1.dds, every non-beast male uses malebody_1.dds, so any change you make to those textures is going to show up on pretty much every character ever. If you're looking to add unique tattoos to a specific NPC, I do have a tutorial written up for that, but it requires the above steps plus using the Creation Kit.

Another question; lets say I have 5 mods that each add a new weapon. Do I need to make sure that when I change the formIDs of the 5 weapon mods to 400000 through 440000 to never use those formIDs for any other future merged mod, or do the formIDs only need to be unique within that specific merged mod?

There are a few armored robe mods already out there, depending on exactly what you want. Inquisitor Set by Newermind43 This adds a standalone set of armor which does have an armor rating, although it doesn't really have much of an "armored" appearance. Robed Steel Plate Armor by MadCat221 Exactly what it says on the tin. It's a hybrid of steel plate armor and mage robes. Skyrim Knights by hideouscircus Based on the above Robed Steel Plate Armor, this adds a bit of variety to the robed part as well as some additional armor materials, (orichalcum, ebony and dragon plate). Black Mage Armor by Reko This adds three armored robes; a steel plate version similar to the above Robed Steel Plate Armor, an ebony heavy armor and an ebony light armor. Tribunal robes and masks by Zairaam One of my personal favorites, as they are hands down sexy. The masks being beast race friendly is a real nice touch. The heavy armor robes requires Ebony Smithing, the light armor requires Glass. Daedric Mage Armor by Natterforme by Natterforme Another pretty straightforward mod, does exactly what it says. Dragonhide Robes by hothtrooper44 The best of the best, (at least as far as armor rating/crafting perks are concerned). Adds robes that are equal to dragon plate and dragon scale. Note this armor is also available in the Immersive Armors mod. Spellbinder Armor by hothtrooper44 Another heavy armor only set that is also available in the Immersive Armors mod. I hope some of those are of use to you.

This is awesome, thank you. Now, for a noobish question; how can I tell if a mod has scripts so I can avoid merging that particular esp?