I'll help as best I can.
Your biggest factor between those companies is the fact that you're going dust to gloss. I'm not too familiar with LMG's final product but between the other two you'll probably see similar results.
Most people don't plug anything other than barrel backs if it's a set. That being said, new anno in the control bore if done correctly
will have minimal effects and i don't think you'll notice any difference unless you go crazy with some digital calipers.
Going dust to gloss won't affect the internals at all. Also, the original anodizing layer will be completely stripped off so the only dimensions that will change will be the outside of the gun and even then it's not anything that will affect performance or even be noticeable to the naked eye.
Yes, more than likely the internal areas including where the bolt goes will be anno'd and it will almost certainly void the warranty. While it is possible to protect that area from the process, i doubt that it would save your warranty.
Long story short, when done properly
, anodizing is perfectly safe for your gun. All dimensions will be relatively the same as before. At least close enough to not make a difference in fit and function.
Edit: There have been plenty of instances of ruined guns which is why I bolded those couple of phrases. If they strip with bleach and anno at 90* I don't want to hear anything about how I said nothing bad would happen.