What exactly should I prioritize when making a kart for 150cc and 200cc and which stats don't matter as much?

I suppose it depend if you are playing with item or itemless. Itemless you have nothing really to hit you and make you stop, so accel may be something less important, unless you are playing 200cc where you have to use the brake, so you have to accel back at your top speed. It would depend on what type of kart you are more confortable with. Don't take a kart with not a lot of control if you can't handle it. You could use this chart to help you build your kart https://docs.google.com/spreadsheets/d/1kfhyD3ZQhfRG0PEZt2Z815K7wZ20R7DOqCQnTBNko0U/edit

I suppose it depend if you are playing with item or itemless. Itemless you have nothing really to hit you and make you stop, so accel may be something less important, unless you are playing 200cc where you have to use the brake, so you have to accel back at your top speed. It would depend on what type of kart you are more confortable with. Don't take a kart with not a lot of control if you can't handle it. You could use this chart to help you build your kart https://docs.google.com/spreadsheets/d/1kfhyD3ZQhfRG0PEZt2Z815K7wZ20R7DOqCQnTBNko0U/edit I mainly do Itemless 150cc. I'm pretty OK with lowmid-mid traction

For 150cc you usually want to build Streetle (Blue falcon is also good but streetle has a tiny advantage) with slick tires and super glider. If you dont have DLC then Pipe frame is what you should go with instead.