this is totally unecessary- almost anything will go through a 25g needle- yet how often, I hear people using 21g or even 20g(cannons). The only reason that I bring this up is that
scar tissue can become a big issue with frequent and/or long term use- USE SMALL
GAUGE whenever possible- which is all the time- if you are injecting suspension heat it
up- it is often granular and if not heated will only go through a large gauge pin. heating it up will cause solute to go into solution.

2. Why is it,or so it seems, that so few use drawing needles?

these puppies are cheap 4$ for a hundred. that way the needle you inject with is clean
and sharp as can be. not only that you can use a 18g to draw- you can draw up anything with 18g in a matter of seconds. its sterile and makes everything easier.

3. why on earth does anyone re-use needles?

Ok, sometimes you run out, this should not happen, but if it does make sure to clean
them with alcohol. other wise just order a bunch when you get them, they are pretty
cheap and range from 12-28$ per 100 depending on gauge, source and manufacturer.
Stock up on pins- dont risk infection for a 25 cent syringe. the doctors visit is going to cost you more than many boxes of pins.

4. injection volume- I often see people posting that they have done several one or two cc injections- heres a little breakdown that may suprise you:

glutes- can usually take 5cc per injection

quads- 2.5 to 3.5 cc considered safe range

delts 2-3 cc considered safe

calves- only if you want nerve damage- not advised

soviets+ eastern bloc atheletes did 10cc injections into glutes and quads- I dont
recommend this but just goes to show the capacity.