Logic Invoice Community

You will need to modify it in the stylesheet.css file, add your own classes and change the colour accordingly. You should avoid modifying bootstrap files.

You can change the auto increment value in the database, so it starts with 1000.

Other changes such as watermark requires customisation.

There isn't such file in the latest release.

config.php file has to be created at the root directory where logic invoice is installed (the directory where you should see the admin, application, system folder etc)

You can also give write permission to the directory, and re-run the installation.

not at the moment, it isn't a functionality built in.

I believe you will need to work backwards, where you will set all the item price 18% less, so the tax is calculated correctly at the final stage.

Admin >> Accounting >> Taxes. You can add multiple tax rates to a single tax class.

Invoice and opencart IDs wouldn't be in sync, but if you wish to, you can adjust the auto increment count in the logic invoice database.

It is meant to be that way as invoice number may not be equivalent to an order number. If you wish to keep both IDs in sync, you will need to adjust the database column to change the auto increment count.

You need to create your own language file translation.