If I MUST Go into the Sun, How Long Should One Stop Using Retin-A Beforehand?

During the initiation of retinoid therapy, you will be sun sensitive. After that initial period of flaking and redness, the skin adjusts and as long as you use adequate sunscreens (and reapply), as well as hats and sunglasses, you are no longer unusually sensitive to sunburning. Most people adjust to retinoids within a few weeks. If you are flaking and red before you go, stop the retinoids for at least one week.

Yes, 2 weeks is plenty. Sounds like you have a pretty good sun protection strategy. Enjoy your trip!

Stop the Retin A about one week before traveling to sunny areas. Use TOTAL BLOCK sunscreen, reapply the sunscreen every 2-4 hours

Two weeks is a good amount of time.  I usually recommend between one and two weeks prior to intense sun exposure. For moderate sun exposure, one does not need to stop the Retin-A at all, just use proper sun protection and avoid the sun in peak hours.

Given that it will be difficult to avoid intense sun exposure on your trip, your plan to use sun protective clothing, eyewear and sunscreens is absolutely great.  That is essential to keeping the benefits gained by using Retin-A in the first place.