Project billing question

We are on R12. We will be using projects billing module to bill our clients for the resources working at client site. We will create a contract project and create individual tasks for the resources that are working in the project. We will get a daily feed with their time that the resources worked on the project that we load into oracle as expenditures. Then distribute costs.  we are not using OTL. We will then generate draft invoice and transfer it to GL and then run the tieback process. Is this the correct sequence. Could someone throw more light. I am new to project