Adapting Single WP site to Multisite WP

Hi, I'd like to change to a multisite before I launch it next week so that it's ready on the correct platform type.

I just need a bit of support on how to do this without losing all my work.

I'm using the help page

Some questions from this page:

1. it states i need to deactivate all plugins.
Question: once I reinstall them will all their configurations remain from previous install or will I have to start again?

I have done a lot of work on the Gravity Form plugin so just need to know if I need to take screenhots of all their configurations.

2. Where it states "2. Add the specified lines to your .htaccess file ". Which lines are they referring to?
I is the same lines that go into wpconfig?
/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );

3. Do i then reactivate my plugins and it should all come back as it was but with the networked admin instead as backend?