NFT Collection Website

I want to sell AChest , BChest , AKey , Bkey nft on opensea. If user has AChest and AKey NFTs together i want to give ADiamond to user. I watched few videos and i understand i need to do things above. If i make something wrong please correct me.

1- Create NFTs and mint them to opensea by using this -
(As i understand i need to use my own contract for users can claim ADiamond from my website wallet)
2-Create website
3-After buy AChest and AKey from my website users can connect wallet and get ADiamond.

For now i just want to list my NFTs using method one. And after i want to complate other steps.Is it possible to complate other steps after selling my nfts on Opensea ?

Yes absolutely you can go through that order :raised_hands: