You'll want to make sure you get the most graphics power you can afford from the start since this can't be upgraded later, unlike memory or storage. If you're on a strict budget, go with one of Nvidia's Geforce GTX 1050 or 1050Ti graphics cards, which will give you good performance on newer games at medium or high settings with prices starting down around $600. If you can afford to spend closer to $1,000, you'll be better off in the long run getting a laptop with an Nvidia GeForce GTX 1060 Max Q with 6GB of memory.
The SteelSeries Sensei 310 is arguably the best gaming mouse for lefties, offering a comfortable design and intuitive thumb buttons, regardless of whether you game with your left or right hand. The Sensei 310's eight total buttons are highly customizable via SteelSeries' Engine 3 software, and the tweakable RGB backlighting is a nice added touch. Most importantly, the Sensei 310 is fast and responsive, making it easy to snipe enemies or command units no matter your dominant hand.