For RAM? It mostly depends on your motherboard. You probably won't benefit very much, if at all with more than 8 GB.
For graphics? If your motherboard supports PCIe x16 cards, there really isn't a limit here, then. If you're buying a brand new card, you may benefit from a GTX 750 Ti or an RX 460, getting the cheaper one. If you're going used, you can get a Radeon HD 7870 or 7850 for fairly cheap.
I'd personally consider upgrading to an Intel Core 2 Quad Q6600 if it's possible to get your hands on one. This CPU, while it has aged quite a bit, is still a pretty decent quad core.