Near Alafia trail system you have AJ's bike shop on Bloomingdale ave 813-685-2453 and Brandon bike works also on Bloomingdale 813-685-3104.
As far as park choice -- Alafia is great and I could certainly ride the whole weekend there. If you want change Boyette is close to Alafia. It offers some nice single track and a couple of intermediate type trails. Be aware that there are no facilities at boyette to speak of, just one port-o-let. It is also an approx 2 mile ride from the parking to the trail head. We also have Trout Creek/Flatwoods if you want easy single track to ride. It is a nice park with facilities, it also has a paved 7 mile loop if you want to rollerblade or *gasp* ride a road bike.
To Boyette from Alafia -- Make a left out of Alafia park. About 1 mile down make a right on CR 672. Stay on CR 672 for about 5(?) miles until you get to Balm Boyette rd. Make a right and park will be on right about 1-2 miles in.
To Trout Creek/Morris Bridge -- Take I-75 north and exit at Fetcher ave. Make a left off of the exit ramp and park entrance will be on your left and right about 150 yards down. Be aware that if you want the paved loop you will need the entrance that is a few miles down fletcher on the left.