Lots of good advice here, but I’d run with 25ga pins as the 27’s you’ll probably be having a long ass time getting anything over a ml in. I use 25 and they’re perfect.
Hey bro, that's completely cool. Here's a tip. Even though a lot of us here have a lot of experience with all this and try and guide new people based on our experiences, there's only one way to know what's best for you. And that's to try it for yourself.
Lats is an other good spot indeed. Theres two ways either with the arm up or across the chest. Personally I rather the arm across the chest I find it's more comfortable.
You definitely don't want to always be pinning the same spot. The more in rotation you have the better in imo. Pushing a pin through some scar tissue gives me the same feeling as nails on a chalk board. Feels like you can almost hear the crushing.
This happens once in a while, Knick a vein, more than likely it’s a bit of the blood clotting up under the skin. Keep an eye on it but I’m sure it’s nothing