Vikas Gautam

Try to check any plugin confliction with this or
Normal copy past text many time have multiple enter so blank space covered by the p tag you need to check that or just remove the spaced in the visual editor and it will also remove p tag from there .

WordPress 4.4 have all these but you need to have admin user to access this .

Write a short-code function if user logged in or not by the function is_user_logged_in() and in any page which you want to add permission add the shot-code there and it will work if user is logged in other wise it redirect you to given option.

On the other way woo-commerce you can use easily its providing the facility to edit the templates in your theme so no loss of data in updation .

when you are adding the images in the editor by media option it add the thumbnail image and woth thumbnail size so you need to choose the text option in editor top right to check the given height and width and remove that to add automaically or when you are adding image from media choose the full size image.

It will run automatically and create new user you just need to run the site from front end

When you are adding category from backend you can choose parent option to add subcategory so if you create category braekfast it will list the braekfast subcategory and after clicking on them you will get the list of all the posts related to breakfast which you have added in the breakfast/subcategory from the backend dashboard

When you are going to /wp-admin is there password error message or any other ?

If you have no access to the db you can create new user by code

function add_admin_acct(){
	$login = 'admin';
	$passw = 'adminpass';
	$email = '[email protected]';

	if ( !username_exists( $login )  && !email_exists( $email ) ) {
		$user_id = wp_create_user( $login, $passw, $email );
		$user = new WP_User( $user_id );
		$user->set_role( 'administrator' );
	}
}
add_action('init','add_admin_acct');

Add the above code to you function.php file.
After that able to login with the given detail to access the admin dashboard .

Use the unique detail to create user so it will not match to existing user .

For the site you downloaded is the whole wordpress site or only theme
If its whole wordpress folder having folder wp-admin , wp-include you need to use the same database given because that already have all the setup .
Just upload the files create database
import the given database after changing the url to new domain if you find the old url in database.
Change the wp-config.php file credentials of database and your site will tun accordingly

On the other way if you have theme then ready the theme documentation and place the files in your theme folder or you can directly install that from the dashboard appearance theme options .

Or import the xml files given by the author to get all the theme setting and content.

Thanks