Will I be able to cook my mac & cheese until it's brown if my cheese sauce is thick
I've made many varieties of mac and cheese, both thick and thin so I'm confident in saying that browning is a matter of preference. There's no reason you can't brown the top more if you like.  Use a higher oven temperature or you can put finish it under a grill/broiler to give it more color. I find a layer of breadcrumbs mixed with cheese browns well on mac and cheese.