Can't be bothered to actually translate everything, just listing some interesting stuff I noticed when reading them. Mostly the stuff I already tweeted but rewrote bits for clarifications and added a few details that I'd previously left out for some reason or another.

Fou and Mashu to scale

https://twitter.com/HccvJPE8Dk/status/764726053193383936

Mashu wasn't made up for GO, they had her concept in the planning stages for SN (a sci-fi looking servant hitting things with a shield). The glasses were added in GO though.

The Saber summoned in GO HAS been through SN, and even brings along and sleeps with a plush lion Shirou gave her.

Agravain gets a special mention in Saber Alter's profile (he makes her laugh).

Caesar

https://twitter.com/HccvJPE8Dk/status/764736045619355648

Shimadrill's comment says Caesar being fat was in the order he got.

Altera was "found" by the Huns, wasn't actually one of them. No parents, no known past. The markings on her body (the 星の紋章/star emblems or stellar markings or whatever you want to call them) were there from the beginning, too.

I think this might be old info but yeah, Iskander/Alexander's horse is a heroic spirit

One of swimsuit St Martha's skills (水辺の聖女/waterside saint) is listed in the regular version's profile but says "not used in F/GO" (Guess the book was written before they had the summer event fully planned). She has an alternate version of Tarasque where it's used as a shield too.

Caster Cu Chulainn has a second NP where he uses all 18 runes to use the power of Odin. Damage, buff cancel, status rank down and temporary disabling of enemy NP (two turns). Anti-castle, max 500 targets.

Hassan yelling "◼︎◼︎◼︎◼︎◼︎◼︎◼︎" when fighting Saber was supposed be "a line praising his god" (Allahu Ackbar?) but they deleted that for reasons.

Kintoki's masakari can power up to 15 charges by loading cartridges. Golden Spark uses 3. But it jams a lot. His real wish for the grail is the resurrection of Shuten; He claims this is because even if he has to kill her he wants it to be in a fair fight.

Vlad is a noodle man

https://twitter.com/HccvJPE8Dk/status/764773864211525633

Most characters get 2-6 pages of art, but Darius III gets 12 (two-page spread for his NP's cut-in illustration, two pages for the elephant, two pages for his cronies).

Jeanne is secretly happy about Alter becoming a servant, sees her as an obnoxious little sister.

Artemis mentions "us" (the gods of Olympus?) fighting an Altera before who may or may not be this same Altera. Also, the current Altera was "excavated" from some ruins. Also, Artemis has an NP in which she uses Orion as an arrow and shoots him at the target's groin.

Mary died of a fever in prison, while Anne's father got her freed.

Scáthach is said to "seemingly has another, higher, body/spirit base (霊基; I vaguely recall this having "saint graph" as furigana at some point but I might be mistaken)- Some say that her name comes from a northern titan, a mountain goddess."