A. It won't; the requirements state that the application should talk directly to the HR systems' database
B. You should ensure your naming convention for the database as clearly as possible so you can rework your data calls with minimal changes
C. You should implement the Repository pattern with the current HR system being the first repository that is built. When the second system comes online, you implement that data access using the same pattern
D. You should map the model directly to the database calls, anticipating that you will have to change the model as the new system rolls out