I think all your names are quite nice.
[name]Arthur[/name] I feel suits a middle name that’s a bit more modern since it does have a bit of an old-mannish vibe to it.
Suggestions: [name]Arthur[/name] [name]Elliot[/name], [name]Arthur[/name] [name]Grey[/name], [name]Arthur[/name] [name]Finn[/name]
[name]Luca[/name] needs a name that is strongly masculine as some people might mistake it for a girly name.
Suggestions: [name]Luca[/name] [name]William[/name], [name]Luca[/name] [name]Frederick[/name], [name]Luca[/name] [name]Thomas[/name]
[name]Nathaniel[/name] is a solid classic that could really go with anything.
Suggestions: [name]Nathaniel[/name] [name]Zane[/name], [name]Nathaniel[/name] [name]August[/name], [name]Nathaniel[/name] [name]Luca[/name]
[name]Matthew[/name] is a classic, but a bit boring in my opinion. I’d pair it with something really fun and unusual.
Suggestions: [name]Matthew[/name] [name]Aurelian[/name], [name]Matthew[/name] [name]Cosmo[/name], [name]Matthew[/name] [name]Ezekiel[/name]
[name]Thomas[/name] is also a name that could go with anything.
Suggestions: [name]Thomas[/name] [name]Paul[/name], [name]Thomas[/name] [name]Alaric[/name], [name]Thomas[/name] [name]Indigo[/name]
[name]Cora[/name] fits best with a longer middle name in my opinion.
Suggestions: [name]Cora[/name] [name]Evangeline[/name], [name]Cora[/name] [name]Rosalind[/name], [name]Cora[/name] [name]Marigold[/name]
[name]Vera[/name] is gorgeous, and fits with lots of names.
Suggestions: [name]Vera[/name] [name]Margaret[/name], [name]Vera[/name] [name]Helene[/name], [name]Vera[/name] [name]Clemence[/name]
[name]Rose[/name] also suits a longer middle name (and I love it in the front spot!).
Suggestions: [name]Rose[/name] [name]Alexandra[/name], [name]Rose[/name] [name]Marietta[/name], [name]Rose[/name] [name]Fiammetta[/name] (saw that in your sig and love it)
[name]Hope[/name] you like some of them 