You can sell stamps that are less than 100 years old to the international buyers. You cannot sell any collectible that is more than 100 years old to any buyer outside India. It is punishable by law. Irrespective of your scale of business, you cannot sell anything such as Stamps, Coins, Collectibles, Documents etc that is more than 100 years old to anyone outside India. You can sell all of these things within India.
To receive money in your PayPal account you need to ask your customers to pay you via invoice. You cannot ask Person to Person payment now. You can't received even USD 1.00 as P2P transfer via PayPal now.