You need to determine how much you plan on spending before you start planning on what to put in. Be realistic about it. Contact 1 or 2 contractors in your area to give you ideas after they look at it and give you options. You can spend a lot of money or less. What is your ROI? It does no good to put in high dollar equipment and you get it repo'd next year because rent won't cover what you spent to buy and fix up. As one of my former bosses told me one time, "This isn't a non-profit organization, we're here to make money."
I like DIY'ers. They pay better to fix.