I think you need to read through my post again.
I'm not sure what species of mantid you have, but you don't need to bother with flies if they are a large species. Though crickets have gotten a bad rap, they aren't THAT bad. If I had nothing but mealworms and crickets to feed my mantids, I'd pick crickets as a staple, without too much regret. The chances of a cricket harming a mantis is VERY, very slim. An experienced adult or large juvie should have no problem catching and immobilizing crickets, and even if bitten, the injuries should not be dire and should heal with the next molt if not an adult. It's more risky with a younger nymph, or especially if you leave crickets in with a mantis who is going to molt. (Which will at that point eat no food) As far as crickets killing mantids with their bacteria, or the black liquid the mantis pukes up after eating one, you shouldn't have to worry about it too much unless you buy storebought crickets or do not keep them in good conditions. You can buy some from the store and keep them clean and well fed off healthy foods, as well as removing frass and the dead. After a week or two they should be more than fine to feed to your mantids. Another option is ordering the crickets from ghann's cricket farm. Apparently, they now carry the newer, somewhat larger, and much more robust and resiliant Gryllus assimilis.
As far as roaches, you live in Florida, it's just about down right immpossible to get any roaches shipped here, since it's illegal. There are some native species legal to be ordered in, but even then I've had people refuse to sell me any. The natives/establised non natives are - Panchlorea nivea, Blaberus discoidalis, Hemiblabera tenebricosa, Pycnoscelus surinamensis, and a few others that aren't popular in the hobby or I can't remember.