Lost in .htaccess : a lot of changes to do

[ Moderator note: moved to Fixing WordPress. ]

I’m going to do huge changes to my website:
– changing from html to wordpress php website
– changing from http to https
– changing all the urls of my website
– Moreover I’ve seen that google is returning results for my website/page.html and http://www.mywebsite/page.html and I want to unify google search results between http://www.mywebsite and mywebsite (with or without www)

and I need definitely some help for the htaccess not to loose my seo. I’m quite scared !!!!!….

Right now, my html website has the following structure:
index.html/ FOLDER/ and inside all my html files

In the future, my WP website is going to have the following structure:
index.php/WP-Folder/ and inside all my wordpress files
This index.php at root will be:
<?php
header( ‘Location: /WP-Folder/’ );
exit();
?>

Inside WP-folder there is the htaccess created by wordpress and I suppose this is where I’m going to add all the changes I want to do for the redirect 301. Here is the code of this index.php right now:

# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /WP-Folder/
RewriteRule ^index\.php$ – [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /WP-Folder/index.php [L]
</IfModule>
# END WordPress
—————————————————
My question is:

Can I add before the “# BEGIN WordPress” the following lines in order to do the several complex redirect 301 (from http to https ; from html to wordpress ; from old url to new one ; from www to non www )?

Exemple for 2 pages:
Redirect 301 http://www.mydomain.com/FOLDER/Page1.html https://mydomain.com/WP-Folder/NewPage/
Redirect 301 http://www.mydomain.com/FOLDER/Page2.html https://mydomain.com/WP-Folder/iNewPage2/
Redirect 301 http://mydomain.com/FOLDER/Page1.html https://mydomain.com/WP-Folder/NewPage/
Redirect 301 http://mydomain.com/FOLDER/Page2.html https://mydomain.com/WP-Folder/iNewPage2/

Thank you A LOT in advance for any help !
I know it is a little bit complex but this is why I need help…
Ana