1. Budget them separately (different fund centre, fund source, or whatever)
2. Yes, you have to assign the budget, unless you exempt through AVC strategy, these FM assignments from budget availability check
3. Commitment items are better to be the same that you would use for new POs. You'd better operate with fund centre or fund source for these old documents
4. Yes, if you don't want to present this budget in the report, you would have to exclude this fund centre or fund source.