Dumping $50 worth of fans into a budget case kind of defeats the purpose of getting a budget case in the first place. But I think you do need at least 1 more fan.
Top rear exhaust and front low intake are the minimum case fans for a gaming build I think.
And a 3rd fan wouldn't be a bad idea either. Top of case, set up for exhaust.
$20 for two fans, and do some testing, then let the results of the test let you know if you need more fans. I don't think you will.
Those CM R4-S2S-12AK-GP are a constant speed fan and come with a 3pin power connector so you can plug them into the motherboard fan headers.
The also have a 3pin-to-4pin adapter in the accessory pack to let you use a direct connection to a PSU 4pin molex connector. A nice option to have.