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Hi there! Welcome to the RPC!
I'll try to touch on a couple things quickly, but please always ask questions! ...or search. Both are good.
Namedays are purely gameplay fluff for the most part. You won't see any gameplay differences on your choices. (Yeah, there's that tiny smidge of elemental resistance, but it's negligible). I haven't seen anything in the lore book as of yet on it, but I could have simply not scoured the right pages.
For Xaela names, think of them as clans/tribes. Your character would probably recognize them if they were from a smaller clan, but from a larger one, less so. It does provide a good way to network with people! If you're ever unsure, I'd recommend sending the person or people a /tell, which is the FFXIV version of a private message. You can find more information on Xaela names here on the official forums and here on RPC.
You can find a bunch of great starter lore by Sounsyy here:
Eorzean Lore Starter Kit
-Racial Lore Compilation
-Class/Job Lore Compilation
-Hydaelyn Geography Lore
-Settlements in Eorzea Pre-Calamity
-Eorzean City-states' Political Structures Lore
-Eorzean Units of Time and Measurement Lore
I'll try to touch on a couple things quickly, but please always ask questions! ...or search. Both are good.

Namedays are purely gameplay fluff for the most part. You won't see any gameplay differences on your choices. (Yeah, there's that tiny smidge of elemental resistance, but it's negligible). I haven't seen anything in the lore book as of yet on it, but I could have simply not scoured the right pages.
For Xaela names, think of them as clans/tribes. Your character would probably recognize them if they were from a smaller clan, but from a larger one, less so. It does provide a good way to network with people! If you're ever unsure, I'd recommend sending the person or people a /tell, which is the FFXIV version of a private message. You can find more information on Xaela names here on the official forums and here on RPC.
You can find a bunch of great starter lore by Sounsyy here:
Eorzean Lore Starter Kit
-Racial Lore Compilation
-Class/Job Lore Compilation
-Hydaelyn Geography Lore
-Settlements in Eorzea Pre-Calamity
-Eorzean City-states' Political Structures Lore
-Eorzean Units of Time and Measurement Lore