Not a good idea to split fan off cpu fan header. Mobo fan header has certain power draw safety limit.  Using Y split off can potentially overdraw current and burn off the header. good thought to add front intake fan.  You can use a sata to 3/4 pin fan adapter if you only use one sata for ssd leaving a second one free.   [IMAGE]   [URL] good idea to mod the side panel to make an air vent such as drilling an array of holes.  [IMAGE]  
Two years ago I purchased one of these computers. Previously I had an excellent experience with a HP Pro SFF with an ancient Intel C2Q, so when I saw the still tinnier and more powerful 3060 I can't avoid to buy it. Later, I realised some issues, first one is the bad MB design with the PCIe x16 too close to PSU, so I had to sell my MSI RX 550 LP and I bough a GT 1030. This year I read about the good performance of new Quadro T with chip Touring ( like RTX 20X0), so I bought a T600, a surprising 40 watts graphic card with 4 gb DDR6 and an impressive performance, similar to a GTX 1050 Ti but with less power drain. Now, system works flawlessly in almost all games. Maybe I'm a bit maniac with temperatures so I don't like my T600 working at 80 ºC or more, same for the micro, a i5-8400. My idea is add a Noctua 80 mm in the case front, in the space it has near PSU for shove some extra fresh air. Also I've think about to drill part of the case top cap. I would know what do you think about these modifications, and if they are really effective. I would to keep this tiny PC if possible. Other question: Can I use the intrusion connector for plug the fan there? The only fan connector I see is the CPU fan connector. I don't know how work CPU fan and case fan sharing the same plug and connected with a splitter fan cable. Thanks for your answers.
How to improve airflow in a Optiplex 3060 SFF?