Internal Networking - Best Practices?

Hi all - i'm in a relatively large financial services company and want to start getting to know other departments in the firm. Have a few questions in terms of networking:

• Should I start out by reaching out to analyst-level colleagues or do I start at associate/VP?

• Would it be inappropriate to ask that analyst for a warm introduction to someone more senior?

• How often should I generally be checking-in with people i've previously networked with? annually or more frequent?

Background: I've already gotten to know the majority of my current department, everyone from analyst up to MD. Looking at other departments to just become aware of the different roles out there that I may try to move laterally to.