You can see the list of preferred servers here:
https://na.finalfantasyxiv.com/lodestone/news/detail/80cd4583bf743600105b947d6906d0909189e479

In a few months SE will create new data centers and give us free transfers for 2 weeks. You can use the Road to 60 bonus to level up on Zalera (the bonus is really helpful to level up crafters and gatherers) and then transfer when the new data center is up.
Keep in mind that we'll be able to visit other servers in 4.57 as long they are in the same DC.

About server population you can have an idea from people who gather data from Lodestone. We don't have any official data from SE.
There's a post on Reddit that shows Lucky Bancho's census but like the title says, it's unofficial.
https://www.reddit.com/r/ffxiv/comments/ab9m7n/lucky_banchos_unofficial_census_january_1_2019/

Anyway, I hope you enjoy the game. Welcome to FFXIV!