HI Rich and Elaine! Welcome to the forum,
1. I'm using a regular travel agent that I'm friends with but, she's located in NJ.
2. I'm sending out Save the Dates right away (I just picked my resort last week so i'm sending Save the Dates this weekend). I'm making little magnet Save the Dates but also sending a letter with price information, resort info, my travel agent information, and my contact information. Will also enclose a little sheet I made from the resort website that has all of the room details, restaurant details, and other resort details. This way all my guests will know how much to save, when they need to take off, etc. There's a section on this forum for Save The Dates and Invitation information you should check.
3. and 4. I'm getting married in Punta Cana but looking through this sight I did see a lot of posts that were brides who got married or getting married at the Dreams in Cabo (they all made it sound wonderful) Definately look through them. Might even be posts for the Riu in Cabo too.
5. I looked on The Knot website and it gave me all the info I need to get married in Punta Cana, my wedding resort actually gave me the same info on their website.
I just picked my resort last week and let me tell you once you pick it, everything gets a lot easier (at least so far). Good luck!