As others have pointed out, you want to be sure to treat within the first 14 days, be sure to initially complain about everything that hurts (even if you think it will resolve), and have a medical doctor give an opinion it was an emergency medical condition - then you could still get potentially $10K in medical bills covered, subject to a possible deductible. If there is no emergency medical condition and/or initial treatment in the first 14 days, then benefits will be capped at $2500.
In a release it usually just means it is a "compromise". They pay you "X" and you agree to accept it in lieu of further pursuing any claims/rights you may have. No one has forced you or them to agree to the terms.
As others pointed out, unless someone other than your employer is responsible, no. WC is a statutory creation. You get x and y, and that's about it. If you don't already have one, you really should consult with a WC attorney, especially given the state of the current law.
You should call a personal injury attorney to discuss. If he hasn't done so, he needs to get treatment right away. He's essentially got two cases - a workers comp and a third party claim, both of which need to be addressed.
For the MD WC, yes, you would likely need a MD attorney. However, if you have had a new accident while here in Florida leading to new and/or aggravated problems, then call a FL personal injury attorney for a consultation.