It is definitely possible to build a semi-passive rig that gets good temps under heavy load.
I'd say your parts list generally looks good for a semi-passive rig, however in terms of the case, while I really love the R4 I don't think it's ventilated enough for decent passive cooling, as with a passive build you really want to be as close to "open-air" as possible.
Also with the CPU Cooler, ideally you want it to have the biggest heatsink possible that you can fit in the case. Check out some of the fully passive coolers like the Nofan CR-95 to get an idea of what a fully passive build would look like. As you don't need the rig to run completely passively under heavy load, you won't need to go quite that big, but basically the bigger the cooler the longer it will stay passive.