I'm not a gunner, either, but there is theoretical knowledge that I posses and I will share it.

-As for the set, Chaos gives a heavy edge with it's CTR and DI, though it should be noted that it also buffs other weapon types, which means that bringing a Final Flourish, Gran Faust, Swagger Storm, Voltaic Tempest, et cetera wouldn't be a bad idea.
An alternative to Chaos that doesn't give CTR but without negative resistances is Shadowsun.

-Don't use the CTR trinket. Since you're wearing full Chaos and your weapons are presumably fully heated, get a Penta-Heart Pendant instead. Although I guess an ASI trinket is an alternative. Health is key in LD, though.

-The weapons is the hardest question to me, as I'm not experienced with LD gunning. Keep the Alchemers, preferably two of them, to switch-shoot. I believe any combination with those would be great.
Storm and Hail would mean you could inflict a lot of statuses, probably forcing your enemies to retreat. Or maybe you can freeze them, load a charge and shoot them again, freezing them once again and/or killing them or forcing them to retreat due to low health.
Storm and Nova would deliver the most damage. It should be noted that Storm has quite the devastating status that is not very resisted at all, compared to freeze.
Lastly, I don't know what Hail and Nova could achieve but anything is deadly in the hands of a good switch-shooter. There's always freezing and then shooting a Nova charge, I guess.

I'd drop the Valiance in favour of another kind of weapon if I were you. Maybe an Antigua for breaking shields, a Callahan for packing a piercing punch, or maybe a Polaris for great denial of area.

Do consider making an Umbra driver as a replacement for the Nova, seeing how the three Alchemers you have share damage type, resulting in some armour sets heavily resisting them. Some of these sets are all Demo sets, Vog Cub set, one of the gunner sets, Chaos, and more, although those are the most popular ones.

You should've let us know how many weapon slots you use, anyway.
If two, bring an Alchemer and anything but an Alchemer.
If three, I suppose bring an Alchemer, another kind of gun (see two paragraphs ago) and a sword or bomb. Alternatively, replace one of the latter two with an Alchemer for switch shooting.
If four, bring double Alchemers for switch-shooting, another gun of choice (two paragraphs ago), and either a sword or a bomb.

So yeah, that's how a non-gunner views it.

NICKO

i use magma too. skolvers may often resist shock, but fire can also help kill them or get them to retreat (BURNNNNN!!). using magma and shadow driver, i could get over 10k with no slots, wearing shadowsun. if you go recon, i'd probably get asi trinks for some fast gunnin'. in the situation of a recon, if they broke your cloak, youre likely screwed with or without pendants, so i'd go asi to try to kill 'em first. this would be in vice versa (dmg trinks) if you wear justifier. i havent tried chaos for gunning in LD, but theoretically, with all that polaris spam out there, i dont wanna be convulsing from shock.

also consider getting sentenza for those pesky bombers. a decent bomber can easily evade umbra, but sentenza was made to spam! callahan can also punch holes in their faces.