i am not sure if this belongs in this forum. sorry if i placed it incorrectly.

if i am planning to move into another province. i think i should conquer a village, then build a church, then continue conquering other villages in that province. this just makes sense to me.

i am a little impatient so i would like to send some attacks before the church is completed (6 hours).

if i send an attack before the church is complete and it lands after the church is completed; do i fight at full power or half power?
Titus is correct, full power it will be. I would just like to add that you can also use the Paladin for the same purpose. And my opinion is not to build the church at all if you're only planning to take 1 or 2 villages in a province, isn't worth it.