That motherboard isn't great. Has the weakest VRMs of the B450 ITX boards, and the software is poor. I know the MSI and Asus boards are better. Not sure about the ASRock.
Also might be worth looking at SFX power supplies. Not needed for that case, but if you decide to change in the future, ATX PSU compatibility really limits ITX case choice. The EVGA GM series is very well priced at the moment (not available at OCUK).
Just passing on two of the mistakes I've made on my recent build; I wish I'd coughed up the extra for the Asus board an SFX PSU.
On the subject of cooling, cooler clearance generally isn't a problem as there's a specified minimum amount of space around the socket. However, some tower coolers have issues with ITX boards if large RAM heatspreaders are used or the motherboard has large heatsinks near the socket. My Noctua U12S can't be oriented for vertical airflow due to my tall RAM and the Gigabyte board's VRM heatsinks. And when oriented for horizontal airflow I can't get a fan on the RAM side (again, due to the size of the RAM; Team Group Night Hawk).
Generally, top-down coolers are more ITX friendly, both with the cases and the boards. So as with the PSU, if you might change cases at some point then one of these (or just an AMD stock cooler) would be the best pick.