How to disable append URL extension for folders

I have been trying to migrate an old blog from wordpress which has permalink structure as

1. Categories - http://www.website.com/category-name
2. Posts - /post-name.html
3. Pages - similar to categories without url extension

etc..

i've used a wordpress-migrate plugin found on github and created 03.folder3, o4.folder4 etc for each category.
All posts have been migrated to respective categories. I used append url extension as .html
so all posts urls look okay.
But ..category.html is seen in menu which ideally should be /category
how to disable append url extension on each folder but keep it for individual pages inside each folder ?

Also i need to add pages (as in wordpress) without .html extension and also run custom insert php code to make them display content dynamically.
The insert php code will insert content from text files which are changed daily (like a daily tip which changes at 12:00 am midnight).
Also page title (for SEO) should change dynamically at 12:00am to show current date.
These pages should be excluded from .html extension.

I've so far migrated only 2 folders (categories in wordpress) with 70-80 pages (posts in wordpress) each.
Hoping that Grav can handle total 1000 posts and about 60 pages.
I've a 2 cores cpu, 2 gb ram litespeed server

@Turum, Before commenting on your story containing multiple questions, I would like to suggest the following:

• Grav isn't Wordpress
  If not already, it is best to start with getting acquainted with the fundamentals of Grav. I would suggest to read chapters 1 and 2 of the documentation. Pay especially attention to the following topics in chapter 2:
  • Pages - and their relationship with folders. Section 'Listing Page' is relevant to blogs.
  • Collections - About collecting and listing similar pages
  • Taxonomy - Collections of pages with tags/categories (mostly used for blogs).
• Explore a sample blog
  Download and have a good look at the 'Blog Site skeleton' (download) which contains a complete blog site. This will give a good impression on how blogs are build using Grav.

After getting a feel of how Grav implements blogs, you might delve into more advanced features:

• Chapter 3. Themes - Especially about Twig with which you can design the layout of the page (e.g your title/date question).
• Chapter 4. Plugins - To provide dynamic content

I cannot comment on performance, but suggest you have a look at the latest blog from Andy Miller on the upcoming Grav 1.7. About half-way the blog he addresses performance.

Hope this helps...

My simple question : How to exclude folders and few pages from default url extension ?
I need default url extension to be .html for all pages (about 900) but null for few folders and pages.

Rest of wordpress to grav and learning, i'll explore as i work on it

Okay.. i discovered a method myself (not sure if it exists in documentation, as i didnt read it completely).
For individual folder (under admin or its blog.md), Append URL extension : /
This overrides Append URL extension .html which was applied for all pages