Is there an API request that would return the current size limit for file uploads? Or even a webpage that could be parsed? Since that number changes over time, it would be cool to be able to check the current limit before running any automations that send files to my uploads page instead of hardcoding it in.
If not, could there be? 
That’s a great suggestion. There isn’t an API like that, but there definitely should be. There is this help page that you could download and parse if you really want to:
https://help.micro.blog/t/micro-blog-premium/1006
The relevant text is:
There’s a 75 MB upload limit
Great! I’ll use that for now, but if you make something more official please let me know!