How is contextualization not compromise?
Good contextualization is not bringing the gospel to people on their terms. That would be compromise. Biblical contextualization is bringing the gospel to people with their terms. That is why we take our language about the gospel and forms of church that declare the gospel and we adapt them to be understandable to the cultures in which we find ourselves.
What are the biggest challenges a church planter faces?
Himself. Period. Can you die to yourself so that God can do something through and in spite of you? Can you trust Jesus to build the church and not overwork so you won't destroy your health, marriage and family? Can you surround yourself with friends who challenge you and not just fans who like your vision? Are you able to train and empower godly elders who will serve as your equals and will more than once save you and the church from certain implosion?