Sparrows are not entirely cosmetic, the better sparrows have more speed, durability, and some extra abilities (drifting, strafe dodge) that the starter ones do not have. We aren't keeping anything from the beta anyway though, don't get so attached to your things. You'll be able to earn them back quickly and get better loot anyway in the full game, remember we only get as far as level 8, which is nothing.

It really wouldn't be much of an advantage. Most people, including myself, store lvl 9, 10 and legendary items we cant use in the vault. Even if they carry over you'd still have to level your character up to be able to use them. In the beta you earn/find better weapons and gear as you progress through missions and level up. With that being said, somebody playing destiny for the first time when it releases will pretty much get the same weapons and gear as me by progressing through the game. It makes no difference

They could just armour you got in the beta to the full game as you won't be able to use it until you reach that level anyway so there won't really be any advantage. You will get better gear quicker though as there isn't a level 8 cap in the full game so you will be a level 9 and eventually 10 with probably that levels armour so that armour from the beta won't be an advantage for very long at all.

Or everything you're wearing at the moment