New player here. So I'm completely out of room in the weapon storage department and a lot of the clutter is from event and raid SR weapons that I was told to hold in reserve. Don't suppose anybody would be able to help with identifying what weapons in my existing loadout are eligible candidates for skill levelups? I understand that assault is king but am uncertain what other deciding factors there are (if any).

Here's my existing loadout. Please bear in mind that some of the weapons already have been skill leveled somewhat. This happened when I first started out a few weeks ago and hadn't the faintest idear what I was doing. Also, my element focus is lightning.

Questions re: weapon skills - what to level?-untitled.png

Not sure how helpful the picture is so here's a list - thunder weapons only - as well:
Dazzling Gold Carbine +1 (SSR)-(LB0) - Skill level 5
Lightning Drum Hammer +1 (SSR)-(LB0) - Skill level 5
Charles' Thunder Blaster (SSR)-(LB0) - Skill level 1
Side-by-Side +4 (SR)-(Fully LB) - Skill level 4
Side-by-Side (SR)-(LB1) - Skill level 4
Lightning Strike Axe +2 (SR)-(Fully LB) - Skill level 4
Lightning Strike Axe (SR)-(Fully LB) - Skill level 4

Also, not sure if it's relevant by here's my current team:
Raiko - 3/4 stars
Mammon - 3/4 stars
Gryla - 2/4 stars
Baal (story quest version) - 2/4 stars
Off team --- Pluto, Meretseger - 0/4 stars for both

Cheers lads