Let’s see if I can answer all your questions, and if not, please come back to me.
As I see it there are two main approaches if you need to modify the Litium campaigns. First approach is most suitable if you need to change the business logic of the campaigns. In this case you have the possibility to write your own campaigns and campaigns conditions. For more instructions on how this can be done, please look into these two articles:
The other approach, I would say, is more suitable if you are happy with the business logic of the campaigns, but you would like to add a custom UI to support specific user processes of your project. In this case, there is a possibility to add a custom page into the Sales module. By doing this, there will appear a link in the left menu for the module. When clicking the link, there will appear a custom page in the content area (main area of the back office). In this area, you can build any custom UI you want. So, for example, if you need to do some batch handling of campaigns, or anything similar that is not supported as a standard feature, you can use the standard campaigns and Litium API, but add a custom UI to handle the project specific user processes. Read this article, if this approach sounds appealing:
Now to your next set of questions:
1. What happens if you dont fill in how many times the customer can use a voucher code? (Cause the field is not mandatory)
When trying this myself, the field seems to be mandatory
2. We don’t really know what this means when creating a “reduce product price by percentage” campaign:
Yes, you are right, it can be that you need to switch tab to adjust which campaigns your campaign can be combined with.
Is there any plans of adding a search function for the campaigns?
Yes, there is a plan to add a search functionality for campaigns in Litium 8. This version is for now planned for winter 2018/2019. In Litium 8, we are planning a larger revision of the Sales module, the same way we have done for the other modules in versions 5, 6 and 7. Exactly how we will do this is not detailed yet.
Hope this helps, and get back to us if not