Is it for a sloped ceiling?
Thanks for your inquiry. This can be hung on a sloped ceiling.

What type of bulb is compatible with this fixture?
This fixture is compatible with Incandescent, LED, CFL and Halogen Bulbs (60W Max)

Are there any seams on the single drum shade? I see what appears to be a screw on the diffuser? How many of them and do they detract from the look?
Thank you for your inquiry. There is one small seam on the drum shade which doesn't detract from the look. We have sold thousands of these with no issues on the shade.

Does the foggy side of the glass face up or down?
The intended purpose of this fixture is to have the frosted side facing down.

How many light bulbs is in this
The LL-C134 fixture has 3 sockets. The bulbs are not included with the fixture.

Does the glass plate disffuser sit directly on the silver base or does it sit on the white plastic arms ?
The diffuser sits on the silver base.

What is the measurement across the base plate?
The base plate is 5 1/8 inches in diameter.

For the 5 light pendant, can it be switched so the lights are downward?
This fixture cannot be hung upside down.

Where/how do you store extra wire for the drum style?
The extra wiring can be housed in the canopy that attached to the ceiling.

How are light bulbs changed? Unscrew from bottom? Is it open on top...Need ladder to change?
The easiest option would be to change the bulbs from the top of the shade.