1) IM= Intramuscular Sub q= subcutaneous or under the skin. IM after the muscle is worked is best. Then, if you can, do even more work on said muscle. That being said there will be systematic effects. Other body parts worked may also benefit but not nerely as much as the part injected.
2) L-Carnitine L- Tartrate is intriguing. Maybe some GHRP for after.
3) The added strength will take getting used to. You need to be carefull where you inject being as that the wrist/hand has an ass-ton of nerves that could be affected. After the injections you'll notice that area gets 'pumped' easily, this is good. The new muscle fibers are forming and getting stronger and it will take time before you fully realize the results.
4) I'm not positive but I wouldn't think so. You don't have to be in the gym to work your forearm muscles though, so I doubt that would even be a concern.