- Could you tell me how to find the CoS hideout?
Take Devon's head back to Tibbets' Asylum and talk to Doctor Linder there. Once Hoover Dam gets added to the game there will be an alternative way.
- Does it take First Aid OR Doctor to help cure Elder Brixley? (Just making sure so I know which skill to raise.)
Doctor skill but it's a tough 90+ check!
- What is the teaser location you mentioned north of The Reservation?
The Crater!
- Will the guy from the Radspider cave ever be a companion at some point, or does he just exist for the random encounter?
Only for the random encounter.
- How do I find a systolic motivator to repair the suit of power armor? I have found the technical manual already.
Search the teaser location.
- How do you repair the memory banks and water chip on level 2 of the Maxson Bunker? I tried using a water chip on the computer and it did nothing, and repairing the memory banks made time pass but it told me I couldn't repair it.
Your Repair skills is too low. Try again after you level up. Also, keep the water chip you'll need it
- Is there anything else to VACCS other than the one map? (Shack inside fences) What's the point of that location?
It's also a teaser location that will be added after I finish the main game. You can encounter someone there during the night
- In Fort Abandon/Aradesh, is there any point to the ventilation tunnels? I found a keycard down there, but does it do anything?
That keycard helps you unlock the door inside the oil refinery power plant.
- In Fort Abandon/Aradesh, is it possible to clear the rocks in the tunnels underneath the farm to further pursue the Legionnaires with the Deathclaw eggs?
Not at the moment!