Oh my do you need help.
Okay, Magic Beings - it is just a designation, like Undead or Animal. They do have special concerns, so look for the little Fairy icon on the unit and click on it for a description of the important parts. By themselves, Magic Beings can be hit by any weapon, so it's not an issue for that. This is different than Sacred, and different from Ethereal.
Ethereal is a state, that most units do not possess normally. It makes normal weapons pass through them 75% of the time. You do need magic weapons to be effective against them - it's a powerful tool, learn how to use it effectively as soon as you can (both Ethereality, and tactics for killing Ethereal creatures).
As for items you give commanders, I am pretty sure that they are all, by definition, "Magic Items". Number of attacks listed, is attacks per round, that is to let you know if they deviate from 1/round only, unless it specifically states "this attack can only be used once per battle", or has an "Ammunition" listing.
Ghosts and Spectral Whatevers will definitely be Ethereal. Most normal troops that you can train will be relatively ineffective against them. Number of troops isn't the relevant factor, you'll fully understand this the first time you crush an entire army with your Cyclops alone.
You first need to forget "generic armor" on your pretender. Then you need to discover the dividing line between "crappy armor", and "worthwhile armor", try to only ever put the latter on a pretender.
After that, you need to get him scripting buffs on himself. With his high natural Protection, and with good armor, armor buffs will be of little overall use. Try to get Soul Vortex for him, or at least Drain Life. Buffs need only be cast once per battle, but even if there is a second battle in the same turn, the buffs need to be recast.
Any other questions, and we'll try to help.
Though I personally spent a few good months training myself before even coming here, so no one could see me gasping for breath.