S.,
I don't have any experience with knockout roses. I want a gardenia bush but I hear they are hard to cultivate in some cases due to the poor florida soil. I have a black thumb myself.
I just planted some lantana & they are blooming & doing well. I don't recommend if you have dogs because they are toxic if ingested.
I recommend UF's Ag Dept- http://solutionsforyourlife.ufl.edu/
They have a link for gardening.
I also recommend a subscription for Florida Gardening.
http://www.floridagardening.com/
The subscription is $20/year. You can get back issues. I don't know if your local library would have back issues for you to look at or not.
They really stress- xeriscaping- FL friendly gardening.
Now that the states laws have changed (as of July 1st) you can't be forced to have grass lawn, by homeowners associations!!!
Your county extension service maybe of some help as well.
USF has a botanical gardens. Watch in the newspaper for gardening events- they will sometimes have a seminar &/or goodies, plant swaps.
Check Freecycle.org &/ or craigs list to see if some one is giving for selling cheap FL plants that they have propagated. I was given 2 lovely plumeria last year by a co-worker. One of them just won't quit blooming!!!
Good Luck!!