Congrats, and I can understand why your family has concerns. It is a VERY expensive endeavor and excruciating and long process. and Everything costs money. There are so many fees. The police certificate is about 40 CUC and should be ordered as close as you can to when you submit your application. It takes appx 30 days to get one. For the medical, it was 405 CUC but was supposed to go up this January. Again, it is only good for 1 year, so doing this as close as possible to submitting the application is best to avoid it being expired by the time that get to your application, in case of delay.
Be prepared to spend at least 4,500$ just in fees between the wedding doc, notary, application fee, medicals, etc. the first year. This does not include any travel or stays in cuba, or the wedding itself. Factor in all the other expenses for communication with your husband, trips, the wedding, etc, it adds up REALLY fast.
Best of luck to you.