> Is job security at a larger company real?
It varies greatly from company to company. At Google (where I work) yes. At Facebook no.
> What’s the pace like
I often work less than 40 hours a week and nobody even mentions it, but if I work more they tell me to work less.
> Is there really a lot of process that get in your way?
This depends entirely on what you want to do. Do you want to redesign GMail? Do you want to rewrite the codebase in Haskell? Do you want to move your data storage to mongo db? Then yes, there will be a lot of process in your way. Risky things like user facing changes and introducing new unsanctioned technologies will force you to go through a lot of bureaucracy.
But on the other hand if you just want to build and improve infrastructure using company sanctioned tools then there isn't that much process at all, just get a code reviewer and you are done. I haven't been blocked by process for years, I just decide I want to implement a feature, I write the code and send it and the feature is in an hour later.
> Are your peers generally competitive or supportive?
Peers evaluate each other so you don't see much toxic competition. However most of your peers will be relatively ambitious people so they will strive to look better than you, so you could say that they are competitive even though in this competition supporting peers looks good.