First contact a Realtor in Jacksonville to give you a realistic sale price and ask him/her to give you a breakdown of all the costs involved, transfer taxes, etc. Looking at sold properties online won't give you the full picture. Then you'll know how much you need to bring to the table to close the sale.
Then contact a mortgage lender who can walk you through each of your options on the MD house - here's a good one in MD http://www.apexhomeloans.com/allentayman
Home Equity Line - usually a variable rate, pretty low rates right now, but if you're going to keep it for a while the variations should be considered. If you're going to pay it off quickly, then not such a big deal.
Cash out refinance - if this lowers your rate significantly for the entire mortgage, or keeps it close, this is a viable option. If it raises your rate on your primary residence or pushes you into needing Premium Mortgage Insurance (PMI) probably not your best option, but worth looking at.
Second mortgage - my understanding is that stand alone fixed 2nd mortgages are hard to come by these days, but there may be a good option if it's available to you.
It's a pain to be a landlord, but talk to the FL realtor about trends and how values are increasing. If values are increasing, then you may want to also consider holding onto the rental for another 5+ years, then sell or hold onto it indefinitely as an investment.
You have a lot of factors to consider, make sure you work with people who are willing to walk you through all your options and all the details.
Best of luck!