Looks solid. But two things could change. You don't need more than 8GBs if RAM if all your doing is gaming. And you need more storage than 500GBs, that'll fill up fast. Either spend way more and get a 1T SSD or just get a 250GB SSD for the OS and utilities, saving yourself about half the price, and use that saved money to buy a 1TB 7200RPM hard drive.
looks pretty good, but please not that cooler(ik its a best bang for your buck cooler), but it'd be an eye sore in that define r5 especially when you're buying a windowed case, maybe go for either an AIO watercooling solution or a better looking cooler.
Looks good to me, although I'd maybe go with 8GB of RAM from the beginning, if some money's needed elsewhere switching up that storage config (could grab a 1TB HDD for the sacrifice of 8GB of RAM, and keep that 500GB SSD maybe, not quite sure about pricing) - you might not need more and if you find you do, it's not that much to grab another 8GB kit (I mean, here in the UK you can grab 8GB for £35-£40 - not much). If you want to keep that 16GB of RAM though, @Tek_Elf's suggestion of grabbing a 240GB SSD and a 1TB HDD is a good option.
I'm guessing your gaming at ultra 1440p? or 4k? Otherwise that video card is extreme overkill. For gaming 8GB is all you need. Other than that, looks good, make sure you got good airflow because the Define R cases are extremely restricting. Edit: Either that or play on a 1080p 144hz, otherwise if your just on 1080p you will be dealing with some serious screen tearing.