populate multiple items for fields for multiple selected fields

So currently I am creating a billing app, and the way you have to go about inputting information for an employee is you select their employee info and the project they were working on and allocate a percentage for each week for that specific project. What I would like to do is instead of having multiple entries for a single employee, I want one entry where I can populate for multiple projects and percentages for those projects. Projects is currently its own table. % per week allocation are just fields in the main table. Is there a way to do this? Or do I have to enter each project separately for each employee?  The most efficient way to enter data now is to search for the specific employee profile and then grid edit so you can go across multiple projects in one screen. 

Example:
Employee A worked on projects 11 and 12. For week 1, they worked 50% on P-11 and 50% on P-12%, week 2 they worked 25% on P-11 and 75% on P-12... and so on and so forth. 

Also another question is there a way to set a requirement on this form where they cannot overallocate a project (aka be more than 100% for that week for all projects), currently my workaround is a separate table where I take in summary fields to check for the errors and highlight them. I also added a filter to make it easier, but functionality wise it would be best if you wouldn't have to go back and forth between the forms to check and fix issues with the allocation.

Thanks!