How is your planning going? Any progress on a destination yet? I am just starting to plan mine. I have picked Riviera Maya in Mexico. I went to a friends wedding down there a few years ago and fell in love with that area. You mentioned Aruba (I have not been but I know how gorgeous it is!!) so I'm figuring you're looking for a tropical wedding.? Does Aruba have all-inclusive resorts? Most of the resorts in Riviera Maya are all-inclusive, which makes for an easy and stress free vacation for your guests.
I started by finding a travel agent. The wedding I went to was arranged by the groom's mother, who is a travel agent. I decided to find a different travel agent for my own wedding. I searched until I found one that has experience in destination weddings, and who was near me (I'm in Denver metro area). I would recommend finding a travel agent #1. There is info for travel agents on this site. Mine is http://all-inclusivevacations.com/. I'm working with the owner now and he is awesome and has been so patient with me on my search for a resort.
I've been reading EVERYTHING on this site the last couple of weeks and I can say that your budget would work for a wedding in Riviera Maya. I haven't searched other destinations, so can't give insight about Aruba... Many resorts in Mexico offers free wedding packages as well.
4-6 months is a very short time to plan a DW but it's not impossible! Just get a travel agent to help you find the perfect destination and resort or hotel and get it booked ASAP!!! Most places I've seen are booked through June this year, and many stress to reserve your date a minimum of 6 months in advance.
As for invitations and wording, I would say just search this site, there is a wealth of knowledge on here!!!!
Again, travel agent. Can't stress that part enough. A ta can get you big discounts on resorts, find you cheap airfare and keeps everyone organized and together. I was looking specifically for destination wedding travel agencies and most I've saw charge a nominal ($50) consultation fee, which is refunded to you when you book, but they don't make their money off of you, they are paid by the hotels that they book. So don't think of a ta as an added expense, they will actually SAVE you money on travel and make the whole experience much easier on you AND your guests.
Also, keep in mind the weather. Not sure about Aruba, but June - November is hurricane season in Mexico. My friends wedding was Nov , 2009 and Hurricane Ida ripped through the area the whole time we were there. It was very disappointing. Torrential rain the entire trip until our departure day when we were leaving. ;(
Good luck with everything and congratultions!!!!