Never use elix - save the jewels. If you can't finish withount them - lower the difficulty. It's ok, when newbie has problems with advents, do raid events - you need to join and deal at least 1 damage, other people will do the rest or union events when even with weak enough team you may get at least weapon/eydo from personal rewards, union members can do the rest if union is active. Yes, LB the sword, L assault is good.
Fire has some nice enough R himes - like Konohana or Nergal, you may use them in your team too, for example instead of Amon - she is useless. But if you don't have Belial with this team - i recomend you to reroll into 100% eydo or at least 2 same element SSR, because your hime setup is not so good. Reroll guide is in this forum.
How to get a fire weapon - next event is fire union, so if you have strong enough union, you will get MLB pride SSR weapon + some SR, fire advent is in 3 weeks. Do fire disaster raids - there is a chance to get a sr weapon there.