Wanted to get caught up on Swamp Thing before the show starts, am I gonna miss anything important if I skip to #20 when Alan Moore takes over or should I power through 1-19 first?
You won’t miss anything by starting with Moore.
He basically re-invents the character.
Saga of the Swamp Thing Vol. 1 Alan Moore is where I would start
Starting at 21 works well. 20 ties up lose ends from 1-19. You’ll be fine if you read 21-64.
Also, after reading #31, Swamp Thing Annual (1985-) #2 is a must-read before continuing to #32.
What JLWWSM said. I would also recommend you go back and read the Wein and Wrightson issues of the original series. You don’t need to but having that context is helpful.
I started from Alan Moore’s run and had enjoyed it!