8x CD/DVD burner (DVD+/-RW) with double-layer write capability

I can't answer all of your questions,  but I can answer one of them.

The Dual Layer (or double layer) technology is not writing to two sides of the same disc,  it is writing to two layers of the same disc.  A dual layer drive can read/write to single layer discs (I do this all of the time myself),  but to write to a dual layer disc,  you need special media (still about $7-10 per disc) and you actually write to both layers of the same side.

DVD's generall come in single or double sided as well as single and dual layered.  A double sided dual layer disc can hold about 18 GB of information,  but you have to flip the disc over to read the second half.  a Single sided Single layered disc holds about 5 GB,  and a single sided dual layered disc holds about 9 GB of information.  I am not aware of any DVD reader/writer who makes a device which can read both sides of a double sided disc, in order to access the second half of the information on a double sided disc,  you have to open the tray and flip the disc over.  Some DVD movies use the double sided capabilities to give you wide screen on one side,  and full screen on the other side of a single disc.