Good evening lads. Completely new player here, had a few questions regarding the whole weapon and eidolon business.

So I went with the lightning element because it sounded interesting. And because my reroll start borked up the Kirin eidolon.
After playing a bit during the event, I now have two SSR event axes of the holy (light?) variety. Given that they are better than most of my existing weapons by at least 90, should I level them up? Should I melt one of them into the other?
In addition, I also have three or four of the SR event lightning guns. Again, should I level those up as well? Melt three of them into the fourth?

On a side note, is elemental affinity a thing? In the case of the above mentioned event's SR lightning guns, they're better than some (but not all) of my existing weapons. Do I gain more benefit from stacking the guns (base power is 288) instead of, say, the four 290-310 weapons I currently have in those slots?

The same questions would apply to the event's SSR holy eidolons, of which I now have 3. Do I keep and level up the three, since they're way better than most of my other ones? Melt two into the third?

Bear in mind that I'm a filthy casual. I'm unlikely to ever spend money on this game, or invest a significant amount of time in it.

Cheers lads