What do I look for if I need a hangy down light like a pendant or chain to use in a bedroom center of the ceiling situation with a sloped ceiling and I want the light to point straight down, so can't go with flat flush mounted fixture because it follows the slope--where you flip a wall switch and you want the room illuminated just to see well throughout the room, not task lighting, but not intensely bright but not too dim either. How do you choose wattage or size/type of shade and see how much light it throws into a room when a lighting store has them all lit at one time? Is there any resource you know that shows image of how a fixture will actually illuminate a room?

There are many formulas for calculating the foot candle outputs of fixtures in any area. But these won't do you any good. Find a fixture that pleases your eye, put in the largest wattage bulb(s) the fixture allows and go from there. If it's too bright, go to a smaller wattage bulbs. If it's not bright enough, the store may accept a return. But most fixtures for home use have a limited amount of lamp holders. And dimming is always a possibility if the fixture is too bright or you want to adjust the light from time to time. Shaded bulbs are always more subdued, but shades often eliminate shadows. Bare bulbs will be brighter, and of course the light will be more glaring, possibly distracting. And bare bulb fixtures are sure to create shadows.
It's really more of what you want to see than anything else. And go to a lighting store for advice, not a home center. They will be able to answer your questions more accurately than a kid at the local Home Depot. But again, start with what pleases your eye first, then go from there. Good luck.