what I can tell is that the Breton names (after Daggerfall) are based off of Latin. Not in the ways the Imperial names are. Those names are actual Latin. But the way that languages develop. For example, Valtieri is a Latin based name, as is Motiere, and Amelion. But they are not Latin. Valtieri is very much Italian, Motiere and Amelion are quite French. Other names sound to be from that southern European environment. Some may even be argued as Spanish style. Sintav, potentially.
Not really.
Ancient Celtic (specifically: Gaulish, because it's closest) nomenclature is often easily confused with Italic/Latin nomenclature though. Latinization of names often got quite similar results. Often just replacing noun cases would result in a name that would seem like Latin, especially for us. For instance: Mediolanon -> Mediolanum. Latinizing "Amelion" would probably result in Amelius.
As far as your Spanish connection is concerned, most modern Roman languages have Celto-Roman influences related to Celtic origins, with Spanish it's Celtiberian and Hispano-Celtic for example.
Bretagne (also known as Brittany) and the native Bretons are certainly the source of the racial name. However, the individual names I don't believe can be limited to a single region of Europe.
True, as always Bethesda have used their creative prerogative. Especially when naming characters. I don't think Bethesda actually researched names etymologically before sticking them on NPC's and places. Bethesda just used what seemed cool and what seemed to fit. And imho they did the right thing. Frankly I don't care about etymologically correct names, indicating some exact real world group of people whom some Elder Scrolls race has been based on. Just use some usefull influences and make the rest up as you go, it's fantasy after all.
The Bretons of Bretagne still fit best though, roughly, as a source of inspiration culturally.