Cool project @nvysel24 and welcome to OpenBuilds! word of warning though if this is your first build you will be hooked I would say that you are well on your way and a NEMA 17 will do just the job fine for a slow moving camera rig with all the weight you mentioned. If you were moving back and forth with very quick acceleration and stops like on a laser or 3d printer head then you would want to keep the gantry as light as possible but since you are going slow you will have no problems that I can see.
I'll take a stab at the math. This is for a nema17 with 20t gt2 pulley. pull-in torque / pulley radius = belt force 50 oz.in. / .25 in = 200 oz. = 12.5 lb. That's the most it could possibly lift vertically. I'd cut that figure in half for a safety margin.
Yeah, vertical is the worst case. It will carry more at an incline, and even more when level. Exact figures for that involve some trigonometry and coefficient of friction. There's other stuff to consider too. Micro-stepping can drastically reduce torque. I'd recommend a 400 step motor. Then just use half (or whole) steps. My figure for pull-in torque might have been high. They usually don't tell you that number.
