General consensus from people I have spoken to who have crossed the Gulf is 4-5 days (for the Gulf) depending on weather and winds. In July, what would worry me is the threat of hurricanes and you not being able to get to port in time. Yes, we usually don't get big storms until late August and into the fall but this year the water temp is very warm, very early. Is there any way you can delay until November?
Some info specific to Costa Rica- http://www.noonsite.com/Countries/CostaRica
If you are looking for crew, try posting in this thread once you firm up your plans. http://www.sailnet.com/forums/crew-wanted/
SSCA is also a great site to get information and recruit crew.