I have been wanting to write a story for a while which would feature a newly-created terrorist group in a society similar to today's society in the US or the EU.
While I have already outlined the main characters, their motivations, and the structure of the organization (sort of uncentralised, with different cells operating with a common goal but not really requiring approval for making certain decisions) I have no clue how actual terrorist organizations function: how they manage to get guns, how they get ahold of "safe houses", how they communicate, how they share information, how they recruit people or how they move around (stolen cars seem like something easily trackable with all the cameras around city centers, and trains and planes require ID).
I could of course omit all that information and not explain how the hard bits happen, but I feel like the story would be missing too much.
I am afraid trying to investigate this stuff online will land me in an FBI blacklist ("Hmmm, what is this guy doing researching terrorist-organization-creation 101 for weeks and weeks?"), so I have refrained from investigating much. I'm not interested in extremely low-level details, no way I'm writing "They used PGP with 4096-bit long keys to encrypt their e-mails, and only used Signal when live messaging was necessary", but I would still like some information about the bits I mentioned before.
Can anyone provide this information or point to resources that I can take a look at (books, websites, documentaries...)?