comments:
Reroute the wires you have, now, to either come up from below or, if they are long enough, down from above. Then you can populate that side of the case with 3 120's instead of the 1 there, currently. I would suggest something a set of the fans that can link together to avoid extra cables and are all powered by one connection at the end. I dont know what your budget is like but the best inexpensive ones I know of are these ones from thermalright. Higher quality/more performant options that ive worked with and can reccomend are available from thermaltake, lian li, and phanteks while im sure there are a million even cheaper options from your basic big retail site letter jumble brands https://www.amazon.com/Thermalright-TL-M12QW-S-Fan-120mm-Simplifies-Management/dp/B0FB2ZWWXV?ref_=ast_sto_dp&th=1&psc=1