For a new marker in the G4's price range, I'd also consider the Proto Rail, and the Gog Extcy. You'll also want a mask, a tank, and a loader, minimum. Try on masks and buy what feels good to you. Playing with an ill-fitting or uncomfortable mask is pretty unpleasant. Good mid-priced masks include the VForce Profiler, the JT Proflex, the Proto Axis Pro, Empire E-Vents, Invert Avatar, and Sly Profits. If you want to spend a bit more, there's the Empire E-Flex, the Dye I4, and the VForce Grill. If you live somewhere hot and humid, and/or you tend to sweat a lot, I'd budget for a thermal lens as well. The Halo Too is a good mid-price loader. For tanks, I've had good luck with Ninja, Guerilla Air, and Crossfire. Most folks here will recommend a Ninja 68/4500. Before you buy one, check to make sure that a 68/45 fits you well.
One more piece of advice: resist the urge to upgrade a low-end marker. If you're going to spend the money, do it upfront and start with something better like an Axe, an Etek, or a Reflex Rail (or a used high-end like an Ego, DM, or Vice from a few years ago.)