Minimum requirement? You mean level of units or specific units? If it's the former, I guess 50CC40-50 and if it's the latter, then I'd go with this set-up:
1. Deploy any archer/vampire hunter where Fran and Spica are (order doesn't matter)
2. Deploy Prince
3. Deploy Katie/soldier with ReinIII where Bernice is
4. Deploy a duelist with high MR where Lesia the valkyrie is
5. Use your soldier's skill and deploy two healers near your archers/vampire hunters
6. If your archers/vampire hunters and duelist are strong enough, you can skip this step. Deploy another duelist where Sukuha is.
And voila. The rush can be taken care mainly by your front duelist and archers/vampire hunters.