I have fan in low front and top pushing air in. Top one is directly over RAM. Then, CPU fan pushes air to back, where fan at back wall sucks it out. Free flow in from bottom, PSU sucks also air from there and pushes it out from back. Free flow out top rear. Vents at transparent side panel let GPU cooling fan air out. CPU temp stays during gaming between 65 and 72, GPU rarely goes over 70.
My mill is a collection of parts stolen from a museum, but runs relatively well. Tower is from year 2010, mobo and CPU 2012 etc. CPU is Intel Core i7-3770K, "slightly" overclocked, as factory specs are 3.5-3.9 GHz and I run it base speed 4.20 and turbo 5.02. For example War Thunder (my son plays it) with max graph settings keeps around 80-100 fps.