A 3" group is fine as long as you can do it in the field also. There are some people who can shoot a 1" group in the back yard but have a tough time hitting a "8 inch vital area on a live deer. Consistancy under pressure is the key. If you can take one arrow every day and hit your deer target in the vitals every time at 20 yards you're almost good to go.
You'll never know how you will shoot on a live deer until you put yourself
in that place. Keep practicing to tighten those groups to the best of your ability but at the same time learn to stay calm when that big buck is standing 20 yards from your stand.

2" @ 20yrds MOA

Doesn't reallly matter how big your group is because I don't know how you are measuring it. For example, if you were aiming at a spot and all of the arrows are 6 inches away form it, although the group is tight, it isn't where you intended it to be.

Only you know the answear. If your first arrow is on or near the intended impact point then your good to go. If it isn't keep working until it is..
After you can do it with field tips than you have to check to make sure the broadhead of choice does it too..

When your shooting at live game, it's all about picking the correct spot on the animal and hitting that spot..