I feel for you BLD. AirAsia have given me a lot of pain.
Get to DMK early, AirAsia have a lot of early flights and on my last visit their checkin was mobbed. Their app makes it look easy to check in ahead of time and just drop your bags using the bagage tag machines but none of that was working when I was there. Like you I had an overnight stop so when I came in to DMK the evening before I used the AirAsia checkin machines at the south end of all the checkin desks to get boarding passes for the next day. Only because the machines were quiet, being at the opposite end of the building to AirAsia checkin counters. It didn't help with luggage though.
Let us know how the Amari works out. I usually use a cheaper option Louis Tavern not too far from the airport but if I was travelling with a family the Amari sounds easier.