For search I generate a JSON array, with the name and the url to each post. Then I just client side javascript to search them. It adds a small traffic overhead, but users said they really like the search - it is instant and uses fuzzy matching algorithm.
Here is the code I use to generate the array: https://github.com/Stanko/Stanko.github.io/blob/master/_incl...
For comments I use staticman (https://staticman.net/), and it is brilliant. Instead of having a 3rd party comment system, it will issue a pull request to your repo. You can set it to automatically merge PRs or to merge them manually (and moderate them).
The only problem is that because of changes to the GitHub API quotas, their public instance gets overloaded. But you can easily setup your own instance. I use heroku, and their free tier is more than enough for my usecase (I get more than 100k users a year).
I even wrote a short post how to set it up on heroku: https://muffinman.io/running-staticman-on-heroku/
Hope that helps, happy hacking!