Larry, are you new to Opencpn
If so, perhaps a little reading about Charts and how they are handled will help you understand what is happening. OpenCPN
is a very powerful configurable chart reader, but it helps to understand some basics.
The reason you need to open chart files one at a time is perhaps because the Senc file has not been created yet from the charts you downloaded. So you must zoom in too force them to open or click on a piano button.
There is a way to direct Opencpn to process all the files into Senc files but it takes awhile. That is described in the documentation
Please attach a screenshot of "I cannot display large areas of the Gulf Coast"
Have you downloaded those files?
Did you add the path to your chart directories?
Did you make a Chart Group for them?
Did you set the Chart Group active?
Sorry about all the questions, but you'll have to be more specific to get any better help. What OS? What version of Ocpn? would also be helpful.
What are you doing? What have you done? Details....