Hi,
I understand the situation. As you said, Job and Resource cannot exist together in an Purchase Order line.
And as far as I know, Timesheets cannot be linked to Purchase Order. I really think It would be much better if the Purchase Orders and Timesheets were linked. But unfortunately, Timesheets and Purchase Orders don't work together, so I think we have to take the next alternative.
- Use Timesheets to recognize Job Costs.
- Use Purchase Order to process prepayments and accounts payable.
In other words, it separates the job's cost recognition from the accounting payment. There will be double entry of Timesheets and Purchase Order line, but I think that is unavoidable. Some customization can be considered to reduce the workload of double entry. For example, one idea would be to add a "Get resource consumption from Job Ledger" button on the Purchase Order page.
I hope this is useful to you.
S.Kawamura