Re step 10 & 14: Didn’t you ask how to remove Bootstrap in this thread? It seems like you’re not following those same steps that originally worked. You need to remove more than just the first Bootstrap @import line. Follow that post.
Re step 19: If you just run grunt in your shell, the default task that will be run is grunt dev, which will only output unminified JS/CSS assets by default. The only way Roots will tell WP to read those unminified assets is if you have define('WP_ENV', 'development'); in your wp-config.php file (see here).
If you have not defined WP_ENV anywhere then Roots tells WP to look for minfied assets, which you did not build yet. You should be able to test that by running grunt build, which will output the correct minfied assets based on your main.less file and your site should then reflect the changes you made to main.less.
So you have a few options. You can define WP_ENV, but it appears you’re developing remotely, so that may not be appropriate for you, or you can change Grunt’s default behavior from dev to build.
Heads up! If you use grunt watch then by default Grunt will only generate unminified assets. If you want to alter that behavior then check out this recent thread: Add x.min.css & x.min.script to watch.
But seriously, if you are using Grunt then you should NOT directly touch, create, delete, copy, cut, paste, zip, unzip, or modify your main.css or main.min.css. Put that out of your head and get it out of your workflow. It’s akin to modifying WordPress core files. If you touch those CSS files and then subsequently run Grunt, any changes to them will be lost.