2. Yes you can combine items. As for breaking down items ... did we release that update? (Sorry at work, memory is foggy. I'll check)
3. It's mostly just IC realistic maintenance.
4. They can be random - we just knew we wanted at least four so that you could fill your offensive/defensive item slots. But if you have 8 random items, that means you can't apply anything to your stats.
5. Mythicals can only have the magic associated with their species. (No, you can't have normal magic)