1. You can start at 5 if you have bunch of them. I start use rune at 6 most of the time. Also even if you fail you will get rune shards that can be exchange for +1 coupon - 4 shards= 1 coupon. Notice that you will get them only from normal runes not unstable ones. To up your weapon lvl 90/95 to more than +12 it have to be full orange.
2. You can get a free shared storge from story at some lvl so my advice is to check how many runes are tradeable via storge and put them to one with prem rune so you could up from +8 to +10. Then use +11 rune and if you you succed you can sent it to main or scroll it . Also remember not to push your luck and yolo to +12 when it wont be on good character.
3. It will bound but only on 5th star as far as i know
4. Nope there is not. You can try to find some ppl via mega asking about Arena Trade. If can its good to have item that give you 2x win/lose seals
5. There is a lot of party thats farm new maps so you can join to them
6. That one dunno never try
7. Well for start i would say its good to have beginner done coz after that you can dismalt items and craft element stones but dont use all your gold for that.
Ok so thats a bit of what i know hope it even little helpful. And sorry for my mistakes im to tired to check it all