The most important thing you can after promotion is win your home games- Its the bread and butter to survival, make St. Marys a fortress- I'd use the Goals Galore tactic for this.
However, I'd challenge you to make your own tactic for away matches- Anything on the road would be a bonus, so it wouldn't need to be massive. I'd try either Control or Counter-Attacking football, nothing too fluid for me. Put in a Holding DM and make sure the FB's aren't attacking- Winning with your own tactic makes the glory feel alot better.
As for signings, I'd stick with your top performers from League One, and add in some firepower- I wish you luck!