I'm new to writing TOS/AOS (tho I wrote VOY stories--mainly "lower decks" crew--about a decade ago) but I've come to rely on the transcripts at chakoteya.net
, to augment my Memory Alpha surfing. Mainly because sometimes you really do need to see the original context of a line.
Since I'm writing primarily Pike and Number One, I also rely on scripts--both of STXI, "The Cage", and "The Menagerie". Tho when I did write VOY, I kept up a manifest of characters at Lower Decks
which expanded on and continually updated, based on the original Roll call crew manifest. It was really useful for picking characters to flesh out, instead of just creating OCs.
And for my Spock and Uhura stories, I've had a lot of help on the linguistics side of things from livejournal fans
(I primarily hang out in the Trek writing fandom on LJ).