Nailing down a high-quality mouse sensor is tricky without getting hands-on time with a given mouse. The two key sensor types are "optical" and "laser" sensors, but you can't apply absolutes when judging them. Your best bet is to try out a mouse in person, or to rely on formal reviews like ours, as well as online forums, for the skinny on how a mouse feels in specific play situations.
In terms of display size, a 15-inch screen is the sweet spot for a gaming laptop. You can buy larger 17-inch displays, but this can jack up the weight to way beyond 5 pounds. We've seen 12-pound "portables" in the gaming sector that will definitely weigh down your backpack. We recommend at least a full HD (1,920-by-1,080-resolution) screen. Larger displays are capable of giving you higher-than-1080p resolutions, but choose wisely, as a resolution of QHD+ (3,200 by 1,800 pixels, and uncommon) or 4K (3,840 by 2,160 pixels, a bit more common) will boost the final cost twice: first for the panel, and second for the higher-quality graphics chip you'll need to drive it to its full potential.
You'll immediately want to buy a gaming mouse; even the nicest touchpads are garbage for gaming. The Logitech G series has been the gold standard for years; Razer makes well-reviewed mice, too. Depending on how hot your laptop gets, you may want a cooling pad, as well. And if you've sprung for a pricier laptop, you may want a second monitor for some games.
Gaming laptops can put a serious dent in your wallet, with some of the fancier models costing upward of $3,000. But who says that the right rig has to cost an arm, a leg and the soul of your firstborn? Fortunately for the fiscally conscious gamer, there are some sub-$1,000 notebooks that can run graphically taxing games like Destiny 2 and Shadow of the Tomb Raider at solid frame rates.