For your first game jam I recommend using external assets. There's a ton of free assets packs on here. Pixel art can be very time consuming (especially animation) and 7 days is probably not enough time to make everything yourself unless you're a pro or you're on a team that's handling all the other stuff. Maybe make a couple assets yourself to get some practice in if that's what you want to get better at, but shipping something playable and polished will be hard enough even without needing to focus on art.