Nice!
Something you might consider are fans made for 1U server rack cases. They are far higher quality than those CoolMaster fans but they can get loud without some rpm regulation.
These fans are made to run 24/7 in rack servers.
Supply Voltage: 12VDC
Fan Frame Size: 40mm External
Depth: 28mm
Product Range: San Ace 40 Series Flow Rate - Imperial: 23.7cu.ft/min Flow Rate - Metric: 0.67m³/min
Noise Rating: 54dBA
Bearing Type: Ball
Speed controllers are fairly cheap. There is a 4 fan controller here for about $14.
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=40000011&Description=FAN%20CONTROLLER&bop=And&Order=PRICE&PageSize=36