Turf MG Training pdf file dated Oct 2010
Title is Florida Lawns: Lean, Green, And Clean!
From http://polkhort.ifas.ufl.edu
197 pages with pictures, pesticides, fertilizers, weeds, mowing, etc. Warm-Season Grasses
http://polkhort.ifas.ufl.edu/Power%20Point%20presentations/Turf%20MG%20Training%20October%202010.pdf
For your county do a browser search for an "florida extension service" (no quotes) to find a local office. Make a visit there to talk to the people and pick up reading material.

My story. For a few years I paid large local lawn service companies for fertilizing, weeds, fungus, and insects. After my back yard was nearly dead and front yard crippled from a cold winter, fungus, and weeds, I fired the last company. Am now doing all of it myself. I am in mid-Florida, Sumter county, and previously in Panama City. I replanted my back yard, about 2,000 square feet, with Empire Zoysia plugs (12 inches apart), to replace the St. Augustine (Floratam) dead stuff. Started 2/24/2011 with first of 3 sprays of Roundup to kill all vegetation, finished third spray on March 25. March 30 began with starter fertilizer followed by planting the last shipment of plugs -- ended April 15. First mowing, with Snapper RER riding mower, was May 25. The plugs filled in pretty good by September but it will take part of another growing season to completely fill in. I have applied fungus spray and insecticide but not weed killer so far -- very small amount of weeds thus far. I purchased the plugs from Seedland.com along with a 3 inch plugger. I selected plugs because I did not want to do any removal of old vegetation such as is required for sod, my ground was level, and I could do it all myself, at my pace.

WOW! We are in the same position. My lawn sounds JUST like yours. Has TONS of potential, great landscape, but LOUSY grass. Let me know what you find and what works, and I will do the same :) I tried Miraclegro lawn food today just to see if it would make a difference. I really don't want to dig everything up :/

Please post a picture or two (or more) to show us what you are starting with. Crabgrass is a summer annual grass and does not survive when the sun moves into the lower hemisphere. What you are describing as crabgrass cannot be crabgrass; however, it could be something harder to get rid of.

Since you are on sand you don't have to even think about rototilling. Your soil can never become compacted (along with 99% of all lawns in the US). It might become hard, but true compacted soil is something else altogether.

It sounds like your first step is to mow it all down to about 4 inches high and see what you have. Determining what plants (grasses and weeds) you have to start will determine what you need to kill. What are you going to use the lawn for (sports, pets, children, just looking at, etc.)? How much work are you willing to put in for the rest of your homeowner life? Are you willing to water when Mother Nature does not provide? Would you be willing to mow more than once per week? Willing to fertilize every month or just 3 times a season? Are you interested in an organic approach or not at this time? Do you have a homeowner association telling you what you can and cannot do with your yard? All these are factors in turf selection.