HELP - stuck trying to building a royalty company model

I'm building a financial model for a royalty company with a mix of GRRs, NSRs, and streaming agreements. I've found some older forum discussions on royalty modeling helpful, but I'm stuck on some mechanics around cost treatment and deductions. Looking for clarification on how these work and should be treated in a model.

Current Approach:

Streams:

• Model underlying mine production
• Calculate metal/product flows to royalty holder per agreement terms
• Deduct operator payment and applicable taxes
• Question: Do I include cost of selling the metal in the royalty holder's costs, or does the operator absorb that?

NSR:

• Model mine production
• Apply allowable deductions (backed into from historical net portfolio contribution figures vs. actual historial production to obtain a %, straight line the % as production volume changes over the life of the mine)
• Calculate royalty revenue and taxes
• Question: Is reverse-engineering deductions from historical data the right approach, or should I be modeling specific cost categories?

GRR:

• Straightforward percentage of gross revenue with minimal deductions

Then G&A and corporate debt at the enterprise level to acheive the NAV.

Specific Questions:

1. What cost categories should I model for each agreement type? What's typically embedded in the operator's side vs. royalty holder's side?
2. For NSR allowable deductions: is backing into a deduction rate acceptable?
3. How should I handle taxes: asset-level tax modeling, or one consolidated rate at the end?
4. Are there standard cost-of-sale or delivery assumptions I'm missing for streams?
5. Any other cost items I'm missing that should be included or is that everything?

Any guidance would be much appreciated

-a struggling student currently questioning every decision that led to this moment