I use a back quiver and a hipquiver.
Disadvantages of a back quiver:
- it takes some practice to take your arrows out and put them back
- it is hard to see which arrow you take out
- when walking in tight bushes, you hit the branches with your fletching.
- no place for a daypack, or hard to combine.
- when you bend over, your arrows tend to fall on the ground.
- some back quivers don't stay in place, that's why I use a three point loop system.
When you get used to all this and take care, a back quiver just feels more natural for me. I like to go out with my longbow and a back quiver.
However, when going out for longer shoots, I use a daypack. This allows me to take some more things with me, such as food, extra clothing and so one. And last but not least, it has a drinking system with a tube, which you really need on hot days.
Since your back is full then, you need a hip quiver. Now you can see which arrow you take, you don't hit branches with your fletching, and your arrows don't fall out when bending over.
Some have plastic tubes in them, giving you different departments, this might be noisy when you walk, it tends to rattle.
Those are my experiences.
As for an arm guard; I bought one from Scott Teaschner. They are expensive but are extremely good , comfortable and beautiful. They will probably last a lifetime, best of the best.