Playing a pregenerated character is fine. Download one from the web and then maybe tweak a few things, described below, to make it more of a Hollin character.
Wizards of the Coast has some pregens here under "Pregenerated Warriors," "Pregenerated Scoundrels," etc.
Hollin is part Elizabethan London, and Hollin names are often like old English names. The Hollin overview will give you a feel for Hollin people and places names. Silas, Gregor, and Chambers are some typical names for men there, or maybe Ella or Alisandre for women.
So if your pregen has some crazy fantasy name - "Dwarffoot Witchboltbeard" or something - probably rename it.
Hollin player characters are human. It's fine if your pregen isn't human - it will be human in the story.
If your pregen isn't human, it will have race/species abilities that humans don't have. Just keep those. If you want, maybe add a reason why your human character would have those weird abilities to their backstory.
Write a short backstory for your character. One or two paragraphs is probably the sweet spot.
You can work from the Hollin and Balaal overviews if you want. Those descriptions are everyday public knowledge. If you'd like something more secretive or sinister, send me your character idea or class and I might be able to help with something that's not public (e.g. a faction).