Gain Weapon Proficiency-
You must use the weapon for two sessions dealing with the -4 to hit penalty. At the end of the second session you have gained proficiency for that weapon only.
Attacking with two-weapon-fighting-
You don’t have to do a full-round attack to get that second attack with your off-hand weapon. You still need to do a full-round attack to use your multiple attacks.
Add 1/4 of your BAB to your AC (rounded down)-
This is to help with survivability in higher levels where AC does not scale up with levels. Still under testing, will have to make adjustments as it is played.
The amount of arrows you carry depends on the number of sessions the quiver can hold rather than an actual number. A regular quiver can hold 3 sessions worth. If the ammo is not used for the session or only a few shots are used then the session counter does not get used.