x10 pull guarantees you will get at least 1 SR. That doesn't mean a hime, it just means SR something. Pulling 10 times separately might end up giving you 10 R's. It's mentioned in several hidden places, a poor design choice.

It doesn't matter in terms in total but some weapons have additional burst damage effects. If you're changing elements however, that's a different matter.

All weapon skills apply and to all your active himes and soul of the same element as the weapon. That's why you want to use matching elements.

Elixirs can be purchase on the tab on the right, sub menu->shop->jewel or nutaku gold. Not with gems. I highly recommend not unless you have money to spend. You can get elixirs on a daily basis by exchanging advent event materials.

I am honestly unsure of rage throttle myself. Soul mastery bonuses only applies to the soul.

Since you're just starting off, you can just use them as a temporary wep til you get a better one.