BESTA IKEA shelf assembly, clarifying open questions

Hello,

I plan to set up several Besta shelves side by side for my DVD collection. I don’t have the shelves yet, but I read through the assembly instructions online and some things are unclear to me:

1. Do I have to mount Besta shelves to the wall? I plan to buy the 60x20x192cm shelves.
2. What are the two parts (114930) on the back for?
3. If I place multiple shelves next to each other, can they be screwed together?
4. The online planning tool does not accept it if I want to use the ladder with the 20cm depth. It only works with the 40cm depth. Does anyone know why?

It would be great if someone could answer my questions – there might be some silly questions too.

1. Yes, with the base area the risk is too high that it will be accidentally knocked over. 2. Wall mounting 3. see installation manual, last page 4. I think a mistake in the planner, but I don't really know.

...and don't forget that the 20cm deep one is discontinued at Ikea and already unavailable at several stores...