If you’re not already aware, Arcane Ascension and Weapons & Wielders take place in the same setting. The first two Weapons & Wielders books have a frame story where they’re being on told on a train ride between the second and third Arcane Ascension books, and they involve some of the same characters. Reading Diamantine before The Torch that Ignites the Stars adds some extra context to the story, but it isn’t in any way required.
The third Weapons and Wielders book, Soulbrand, is almost finished – I’m hoping to have preorders up later today. More announcements coming soon, too.