1.what does the amount of resistance mean and have to do with the guitars tone?
Resistance is another way to say, in effect, how 'wound' a pick up is. The more wound it is, the more output (hot) the pick up will have. When you read resistance, you would probably notice that single coil pick ups have less resistance that humbuckers and that pick ups made for higher output will also correlate to a higher resistance. For tone...see the next question2. What does "hot" mean and whats the hottest pickup
Jumping from the last question, a pick up that is more wound is 'hotter' and give more output. What this does is essentially send more signal to the amp than a less hot pick up. Hot picks are key to getting a more natural sounding overdrive and make it easier to do so..
'Hottest' pick up depends...non-active versus active pick ups. Active picks (with batteries) theoretically put more sound to the front of the amp because it's using a little extra powered boost from the active circuitry. Example is an EMG 85. For metal, I'm a fan of powered EMG's.
Non-active is something like Seymour Duncan Dimebucker (Dimebag Darrell). I've never heard it and only ran across it recently in looking at new pick ups but I read a little and it's pretty hot.3. what makes pickups distorted like Angus Young signatures?
Lots of stuff comes in to play for an Angus tone but specific to pick ups, see the previous two questions. It's likely the overwound pick up but can also be the type of magnet used too (ceramic versus Alnico). Alnico is said to have a beefier output. I think the Angus has an Alnico V. Other things go in to it such as wax sealing (to protect from pick up 'microphonic' issues etc). An overwound pick up with a 'beefy' magnet is going to push the amp a little more and make it easier to get that warm 'butter' tone with overdrive.4. how do i tell if a pickup is would be good on a custom in the neck position or bridge position?
What will be good depends on what you want. This is not so much a science that as a matter of personal preference. For me, I have a Gibson ES333. So, I'm replacing the current pick ups with a Gibson '57' in the bridge position and a '57T' (Plus) in the neck position. The '57' gives a warm, mellow tone for cleaner playing like in some jazz or less to non-distorted playing. It's cleaner but warm. The '57T' is more wound and give a classic overdrive sound like an early AC/DC (Malcom) or most any other classic rock sound.
So, it's a matter of what you want from the pick ups. You may not even know that now but it isn't a bad rule of thumb to have a less wound pick up in the neck position. 5.lets say i was going to have an Angus young signature humbucker. Would i need one in the neck and one iin the bridge or could i use an Angus Young and another one (like and eddie van halen or or custom)?
Pick ups are mix and match so you can do whatever combination you desire. You can break the 'rules' if you like if that serves your tone needs. Whatever 'rules' there are, you need to get out of your pick ups what it is you want to hear. A few things I said above are rules of thumb that I've picked up over the years but there really is no single path you have to follow.
In the 80's, I spent more money on pick ups that I practically did food (ok, not really...) so finding what you want to hear can often be a little journey of experimentation. Then again, if ya know what you want to hear, folks can guide you to the pick up that will do that.
....what I've said above is, I think, reasonably accurate but others may have more input to give. Still...A little bit of info to work with.