Furinno Luder Shelf Bookcase with 1 Door Storage Cabinet, French Oak

Q: Can this be used horizontally instead of vertically?

Yes! My girlfriend and I have it lying down horizontally with another set of cubes stacked on top of it. Works great to organize gaming consoles and keeps a tv steady

Q: can I buy extra shelves?

I would also buy more shelves if made available. Could easily use 2 more myself. Gaps are far too large.

Q: Can I put another 3 shelf on top of the first one

I wouldn't recommend it. The back is cardboard so it is not really able to be secured to the wall.... it is not a very sturdy item.

Q: Could you flip this so it was actually standing on the base? That way you could change which side had 3 shelves & which had 4?

Absolutely. You can have any of the four sides be the base.We put it on it's side with the four cubes on the bottom. Works great and easy to put together