NG+ does give you all your weapons/armor/resources from your main runthrough. If you're grinding, do as much as you can in the first playthough before doing a NG+ loadout. The good news on the new weapons: base stats are better than anything else. Obtaining them are pretty cheap with the new Champion tokens - just do missions and a few side quests and you'll have at least 3 before you hit the Embassy. Bad news: the ammo types are weird, and the resources you need to craft them are hella expensive. Mind you, you have access to a Sunwing after you reach your base (though you have to run through at least Plainsong to get to it), so you could just fly to the area of the map you need to fight the enemies for your resources to upgrade the new weapons.

But all that leads back to the main issue: it's a helluva grind to upgrade, and the new weapons are hella taxing on resources. Like... Iriv's Downfall sharpshot has the strongest sharpshot bows, so you can, in theory, do INSANE damage with the right coils and valor surge. BUT you can't carry that many and the crafting cost is insane, making you revert to the Forgefall, Delta or Glowblast if you want more than one hefty braced shot. Unless the DLC enemies really need the upgraded stat weapons to take them down (and looking at how Frozen Wilds amped up the enemies, that may be the case), the new weapons may or may not be totally worth it RIGHT NOW.

My humble advice: If you want to wait for the DLC before starting NG+, it may not be a terrible idea. By then, the various patches and balances may be out, more weapons, armors, and balance changes may be applied, and there's more to experience for the grind you already know is ahead.