There is a question I desperately need answered: What is the offset for hangar capacity (the number of Interceptors/Scarabs)? (Like for EUD conditions.) Or, how can I find it?

check the sticky

Yah... I did. It's not there. Or I can't find it.

I'm pretty sure you have to use that unit as a (double-)linked list starting point and count how many there are, ie:

/me does not understand

AT ALL

Remember that I'm a total n00b at this...

Gotta agree with you, Everything they said flew right over my head too XD.

Get Cheat Engine, learn how to use it, have a map where it adds one to the hangar each time you step on a location, and find the offset yourself

You can just detect units (scarabs/int are units) via a normal trigger. If you're asking for the upgrades, here's a step by step guide. If you're asking how many units a particular unit has, you can follow my guide (link is later) and replace "hp" with "int/scarab number"

under http://code.google.com/p/bwapi/wiki/changes116 (in the sticky)

0058CF2C Technologies Researched (SC) (12 * 24)
0058D298 Upgrades Researched (SC) (12 * 46)

That's the 1.16 location, it's probably changed now. Open up datedit, and see the numbers of the technologies/upgrades.
Carrier capacity is 43 under upgrades, reaver capacity is 36 under upgrades. For reference, terran infantry armor is 0, terran vehicle plating is 1.

Follow my guide (also in the sticky) replacing terran infantry armor for hp. Now, once you find it, open up the Process -> memory editor in artmoney. This will make it easier to know exactly where the location is for this patch. Upgrade vehicle plating, then that will give you the length of the upgrade (you should be able to figure this out yourself though, 255 ups is max, so 1 byte each). Now, go over to the reaver capacity/carrier capacity (you can always upgrade those just to make it easier to find.

I could have done this for you, and actually found the real offsets, but hopefully you will now be able to find your own after you do it this way.