Ouch... I thought my micro-ATX was stuffed.
There are a lot to block the air flow in this case, so I think you need some forced air flow (fan). If you don't mind having a fan on the outside of the box, I recommend making cardboard walls to experiment some before you make holes in your box. I think maybe a 80 mm sucking air out of the box next to the processor would be a good start. And maybe another one on the other side of the case blowing air in? I think you need to get rid of the 30 mm, but I'm not sure if it's best to leave the hole open or close it. Some ducting would probably be nice, but I'm not sure if there is place for any.
About the PSU: unplug it for a while before you open it (I test in the morning and do modifications when I come home from work). There are high voltages inside the PSU. Check the size of the PSU fan (I think it's 60 mm by looking at the picture) as well as how thick it is. Many fans are 25 mm, but there might not be enough space for one inside your PSU. On the other hand, if you put a fan on each side of the box, a fan on the outside of the PSU will look normal
Remember that whichever fans you use, you'll need to undervolt it to make it quiet.