You are permitted to do the work yourself, the DOH will be a pain when it comes to getting the permit but it's not rocket science and is rather well laid out in the code. Since you qualify as doing a major repair you'll have to bring it up to current code. Which depending upon where in Hillsborough County you are will mean that if you currently have a traditional gravity flow system it may mean having to change to a mound type drain field. If you currently have a mound that is properly sized for the effluent flow for your house you can replace the tank with the currently dictated proper size. What do you know about your septic system, like year built, tank size, drainfield sqft. Depending on age some of this can be pulled from the department of health environmental health office from where the permit was pulled to build the system. You can get some rough guestimates by probing the ground for the size of the drainfield.
Out of curiosity was your tank a fiberglass tank or concrete?
Regulations are
here
Let me know if there's anything I can do that might be of help, FL has gotten more rain this year than usual, we've gotten better than 2X our normal annual rainfall up here but it's far wetter down in your neck of the woods my Father in Law's fields in Plant City turned to mud.