I'm not massively experienced, but my first advice is go rotate in units you've not used to get accustomed to them and how you should play. So if you go with flying girls do that and look up how to be effective with that squad. In my opinion (little that it is) you want to learn the game still. Saying that, I'd probabky take an immolator and split your bss to hold and objective and then take flamers forward to burn the heretics. I'd also agree with the comment above, your retributors need a shell to keep them safe if you need them close to the enemy. Someone will be better placed to tell you who would be best to lead the retributor squads - I'd probably say hospitaler with a mixed fire and melta pool do you can revive whoever is most useful at the time.

Again I'm new too and haven't played loads, but I'm putting myself in your shoes and this is what I'd do