I've read what I could at the UESP wiki and the contents of the Prima guide. I've searched here but I get so many "hits" that I get frustrated. So...if you know of a place which answers the following, please point me to it.

1. Enchanting apparel: Apparently you get one shot at this (IE one soul gem) so you better enchant your apparel with some big soul? These items can't be recharged...they are what they are once enchanted?

2. Enchanting weapons: Again, the strength of the enchantment is set by the size of the soul originally used, but it can be recharged, after that, with many multiple, smaller souls?

3. Soul gems are used, and no longer available (removed from inventory) when they are used for the original enchanting of an item or for recharging an enchanted weapon?

4. Only 2 soul gems are not destroyed, only emptied of their contained soul, when used...Azura's Star and The Black Star?

So...if I have this correct, you want to have a really awesome soul to do the original enchantments on items, as that is one factor (your enchanting skill being the other) which sets the level of enchantment on the item for the rest of it's existence, correct?

I appreciate your patience, gang.

Azura's star and the black star are the same thing, the black star was just azura's star but defiled by a disgusting man who should be ashamed to call himself a Dunmer.

Cider!, are the rest of my stated assumptions correct?

Also, I found this at UESP:

Note only Black Soul Gems and the http://www.uesp.net/wiki/Skyrim:The_Black_Star_(item) can be used to capture the soul of an NPC, and is always stored as a Grand Soul.

This seems to indicate that there is no higher soul than a "grand soul" at any time in the game?

1) correct
2) Correct
3) correct
4) technically, they're the same thing, but correct
Therefore, your overall assumption is correct. If there's an unenchanted unique piece of apparel (a la ulfric's clothes) you want to make sure you'll be satisfied with the effects you can put on them.

You are correct on all accounts. Enchanting potions can also give you a boost on the strength of the enchantment.

Correct, grand souls are the largest ones in the game. Only humanoids, dragons, mammoths, and a few others have them.