Whats things should I do/buy, before siding with a faction?

I haven't found a list, only 3 things so far:

Getting the companion perk with Danse, because he gets unavailable as companion after destroying BoS. Same with Deacon if you destroy the Railroad. And getting Ballastic Weave from Tinker Tom.

I also buyed every legendary item from the BoS shop on the Prydwen, right after I met Maxson and the crew. But I don't know if some items get available after some quests. I guess, I should visit every shop of each faction before siding with one.

What else should I do and buy? Is there a post/list about that? Couldn't find one. Oh and I almost forgot, I only have the Wasteland DLC so far. Should I buy the story DLCs first?