Bullion coin care
The bullion value of an ingot should not be affected by physical damage; value is a function of weight and purity, not appearance. That said, would you prefer to buy shiny bullion or dirty and scratched? If you purchase coins, their numismatic value definitely will be reduced by physical damage.
Little known fact: do NOT keep silver in contact with natural rubber. The silver gets very badly tarnished.
Regarding the price of large ingots vs small, I can't comment. Best to go to a dealer (Internet or shopfront) and get quotations.
Finally, where will you store your precious metals if your collection grows?
All the best