FIrst, sadly u must face and probably defeat all three bosses from warzone 1-2-3 to actually be able to spend only 10 points instead of 15 in wz 4-5-6 (personal test, im struggling with it yet beside i have way more points than needed), each wz have its own point system and their own entrance, separated into: gnomish (wz 4), dwarves (wz 5), scouts (wz 6)
Second, these points are needed for you the destroy the lava pumps, these systems were created by the combined forces of the alliance to deal with "those below" forces, once you destroy a lava pump 10-15 points will be deducted from that specific wz (depending on if you dealt with the bigfoot burden bosses u will spend 10 instead of 15 points) that allow you to enter the teleport to the respective warzone lasting 8 hours as soon as you enter the wz tp, so you can travel in and out for 8 hours, once your time expires you will need to destroy another lava pump to restart the time.
Third, yes you can accumulate as many points as u want and spend them continuously in the future, you only need to go inside the lava pump's teleport and destroy them, every time your 8h has expired (be careful ppl often to trap those tp really often, is recommended to activate the lava pump at ss time to avoid struggling with this).
Fourth, yes you can give only devices and still be able to spend these points, as long as u have enough points u can destroy the lava pumps.