I. Gunslinger includes weapon familiarity.

I have been made aware that the upcoming GURPS High-Tech will include rules (different from mine, but excellent nonetheless) that make it worth the cost. I'll be using those rules instead.

II. Magery 0 can be limited just like higher levels of Magery.

Since the publication of this page, the GURPS FAQ has been revised to make it canonical that you can apply the One-College Only limitation to Magery 0 as well, which is a good start, at least. In addition, the data files for GURPS Character Assistant now support this house rule fully, allowing all of the Magery limitations to be applied to Magery 0. This bodes well for all.

III. Off-Hand Weapon Training is a learnable perk.

GURPS Martial Arts codifies this as a canonical rule now. I suggested it during the playtest and the agreement was overwhelming. I'm proud to be responsible for this change.