A major shift in a production network, what am I missing?

I wrote a big a big story. Then I wrote an even longer TL;DR. You guys don't care. Here is an image of a Visio file. Thoughts?

Assume physical redundancy has been factored in. I'm shifting a production network from a /16 with a Cisco 5512X doing all the heavy lifting to the outside and internal traffic. The physical part is done and planned for, I'm looking for general advice on what I might have missed or could improve on logically.

This is a pretty small network, less than 500 users. However, for its size, I think there is a wide variety of needs. It's not a sales/marketing network with 90% of the users doing the same thing and R&D guys get to sit in a bubble.

Maybe some VLANs are overkill. Some of the vendors are competitors, and I actually worry they'll try to steal information from each other. It's easier to trust them if I limit their scope. Plus I figure Wireshark will be easier to manage when I'm troubleshooting. Yes/No? Am I dumb?

Also if the Visio File is dumb/bad, sorry it's my first time building a network map in Visio. I'm also pretty dyslexic and I didn't print this while proofreading so I am sorry about spelling/grammar in advance. I like to think I'm smart, so I don't really know what I'm asking for other than I think most of you are smarter than me. I don't want this network to fail or need another overhall in 3 years so please anything I might be missing. Obviously, a lot of information has been pared. If this is out of the scope of this sub (not enough detail w/e) I'm sorry. Happy New Year!