I've no needed to myself, but I have seen other people automate Excel rather heavily through PowerShell. And now you mention it, I probably owe somebody at work a script to do something pretty similar.
The basics of powersehelling Excel are covered
here and many other places.
You should be able to write up something that will collect all the contents of some particular folder which match *.html, then sort them by name or date created or whatever, then pipe that collection into a function that loop through in the order they are given to add a sheet with that content to a new workbook, and finally save it out. With better Excel Fu, you might jimmy it to make the graph for you.
If I write my thing, I'll have half of what you need, making it import html files shouldn't be a big leap.
But the nice chaps at these subreddits will probably sort you out more quickly.
https://www.reddit.com/r/PowerShell/https://www.reddit.com/r/usefulscripts/