I haven't gotten very far into enchanting ... but my question is this:

When I have an enchanted item and I go to break it down, does my enchanting level determine anything at that point

or

is the determination made when I actually enchant something.

Only when you enchant something. All you do is learn the enchantment when you break the item down.

This means, you could break down a sword with +15 fire damage, learn "fire damage" enchant, then apply it to a new weaon (but you have low enchanting skil) and receive only a +10 fire damage on that new item.

When you disenchant an enchanted item you are destroying it in order to learn its enchantment. The enchantment is what it is, you won't learn a better or worse version of it by having a higher or lower enchanting skill when you disenchant something. Your enchantment skill (along with any perks you have taken) will come into play when you start to use those learned enchantments to enchant items yourself.

However IIRC learning new enchantments does give points towards increasing your enchanting skill.

"However IIRC learning new enchantments does give points towards increasing your enchanting skill."

That's correct, so disenchanting has the added benefit of leveling you as well as teaching you the enchantment.

awesome. I figured this was the case but thought it couldn't hurt to check much thanks

Since you are a self-proclaimed "Noob" enchanter I'll add this: don't get Soul Squeezer or Soul Siphon. I got them on one character and they weren't worth it to me.

I looked at that ... Didn't sound like something I'd want, good to know.

Actually, thinking about it I didn't get Squeezer, but Siphon definitely didn't work as 'advertised'. It could have something to do with ability in a school of magic (which were all low on that character), but I still had to recharge the weapons a lot.

I figured I'd get the black star fairly early and also equip my follower with soul trap weapon+gems. My character will mostly be blade based, but some perks in magic as well.

I have never used soul siphon, but if you do the math, it isn't all that impressive.
You trap 5%.
Max soul-charge is 3000. (Mamoths or NPC's for example)
So you recharge a maximum 150. Which is less then a petty soul gem (250)

Now, you can imagine you will use more than 150 on every enemy you see.

since we are sort of on the subject, I've wondered if it might be more adventageous to do my soul trapping through conjured weapons+soul stealer when the enemy's health is low and put an extra enchantment on my main blade instead of soul trap

firey soul burn + nearly anything else is quite nice. However vampiric regeneration with that will leave you with a weapon that needs to be recharged every ten strikes or so. Avoid that one, it really messed me up a few days ago.

I get my soul gems from the invisible Dawnstar chest and other places and I only pick up the ones that already have souls inside.

The Bound Sword is a good way to get around carrying an extra weapon when you do want to Soul Trap something. Just having it equipped in combat can increase your Conjuration Skill. It is possible to wield the Bound Sword as an offhand weapon for a Dual Wielding character too.
Soul Trapping with a Bound Sword does require spending the Perks in the Conjuration tree.