Redmine

Hi, I am planning to provide a solution to a customer which includes a project management feature, and was considering to use Redmine on the backend. My solution would have its own UI, and would only use Redmine through RestAPI. I am not planning to modify any part of Redmine.
My concern is, I believe Redmine is a GPL license, which means if I were to include Redmine inside my project, I would have to redistribute the project itself, right?
If so, redistribution of the entire project is not an option, and I would have to consider another solution.
So I was wondering if there any methods in which I wouldn't have to redistribute the entire project.
I've thought of a few(listed below), but I'm not sure these are correct.

1. Other open source solutions(such as MongoDB) provide drivers which are not GPL, and the usage of these drivers wouldn't require redistribution. Are there any drivers such as this for Redmine?
2. (If there are no such drivers as mentioned above,) if I were to create a driver and use Redmine through these drivers, would the redistribution be restricted to the drivers?
3. If I were to not include Redmine in my project, and use an existing Redmine server hosted by the customer and use Redmine through RestAPI, would the GPL be applied to my project?

Thanks