What's the hole in the intake for....collecting antifreeze

The leak shown could be coolant climbing the threads at that thermostat housing bolt.
I personally think the most common mistake here is not allowing time for the sealant to cure before adding coolant and pressure. RTV = room temperature vulcanizing but... more than temperature is required. It also needs oxygen to atomize/release its vehicle. It can be very slow to cure in many applications. Humid chemical laden air is slower than dry air too.