What to keep track of employee project hours to then do some calculations with the totals.

I have been working on the attached spreadsheet, we have projects that our employees work on. I need to keep track of the hours spent on each. Then I need to combine this information so I can do some calculations, for example based on the total hours spent I can then work out the actual cost spend on the project versus what we have invoiced for this project, like a mini Profit and Loss on the labor only.

I created a different worksheet per employee, I would like each employee to only be able to access there own worksheet, based on some protect or share worksheet rules. I created lists of Projects and Users, so this data is the same in each worksheet. Then I would like the data from each employee (only have 3 at this stage) to collate onto another worksheet, which only I can see, so I can do my total calculations etc. Along with hours, sometimes each project might have extras, this is charged at a certain rate per employee, so on the totals page I will also use this information.

Here is what I have so far. Workings 150514 - sample for expert.xlsx

Hopefully there is an easier way to do this. Thanks in advance.