Some things you may treat simultaneously, but too many things could put a strain on your chickens.
Coccidia come in nine different strains, but not all of them are in your locality. Those in your area your chickens already have in their intestines in tiny amounts, and they are becoming resistant to them. I would treat with Corid unless they are showing symptoms of lethargy and loose stools. If you aren't sure about worms and coccidia, it's very simple to gather random stool samples from your flock and have your vet run a fecal float. It will identify any worms present or coccidia in harmful numbers. Again, coccidia are present in their guts in small numbers and that's normal.
You can worm and do Corid at the same time as they are different meds doing different things. But I would wait until you've done those before doing the pox vax because it's a live vaccine.
If you have any chickens with MG, all the chickens have been exposed and you should assume they are are carriers. A healthy flock will fair okay and rarely become sick, and if they do, it would likely not require an antibiotic, it being more or less like the common cold in humans which we get over most of the time without needing special meds.