Project how many grams of gold you could hold in the future from current holdings and recurring additions. The calculation remains focused on physical weight rather than market value.
When the monthly addition is constant, the calculation simplifies to current weight plus monthly grams multiplied by the number of months.
Your physical gram total is determined by the amount of gold acquired. Gold prices affect the budget needed to buy those grams, but not the grams already owned.
If your monthly purchase amount depends on a variable budget, model several contribution levels instead of assuming one fixed amount indefinitely.
Yes. Use the annual growth assumption.
Yes. The result will equal current weight.
Only if your input weights are already expressed on a fine-gold basis.