When you get an FM3 Visa, you have 3 months from issuance to move your personal used possessions without paying duty. If you get your menaje (list of items being moved, in English and translated into Spanish) approved by a Mexican consulate within those three months, the actual move can take place after more than three months. If you move more than three months after getting your FM3, you have two other options: 1) declare everything you are taking to be worth $999 USD and pay the duty, which will be almost nothing if they take you at your word or, 2) hire an expediter at the border and pay no duty, though you will pay "standard" moving costs for delivery to your home. We used an expediter in Laredo to move us across the border and to the Ajijic area way after the FM3 was too late. She was great and we paid no duty. There is also the 200 peso note hidden in the palm of your hand as you greet the border guards, but I don't recommend that.

As to whether to move a lot or a little, we tried to find a middle ground. Now my wife complains that we should have brought this and we should have brought that. She has regrets about things left behind, so it is best to live first in Mexico for at least 6 months (we were here for over two years before moving our stuff), then to think long and hard about what to move and what to give up.

Good luck!