Set RPCTxFeeCap to something reasonable for large contract deployment. Originally I just went for ETH dollar price/ETN dollar price but i have since divided this by 20 to account for relative appreciation of ETN against ETH. The safeguard is intended to be a $ threshold, so will be around 200$ at current prices, which is plenty for us anyway as network usage will be lower for a while.
The validator set will be widely geographically dispersed, so it's best to include a slight allowance for potential clock drift. Hence AllowedFutureBlockTime --> 5s. Typically a time ~= block time is chosen. Eg Ethash chooses 15 seconds.