Hi @SyedArh ,
For your first question, the answer is YES. You could create a PowerApps Portal based on your D365 F&O data. Currently, in PowerApps Portal, it mainly use Common Data Service as its underlying data source. There is no direct way to connect D365 F&O data to PowerApps Portal.
But the D365 Finance and Operations entities could be configured as available virtual entities in Common Data Service, so you use D365 F&O data in a PowerApps Portal.
Please check and see if the following blog could help in your scenario:
https://www.powerazure365.com/blog-1/powerapps-portal-with-dynamics-365-finance-and-operations
For your second question, currently, there is no public eCommerce websites created using PowerApps Portal has been released.
For your third question, I think PowerApps Portal and Dynamics 365 Commerce are both OK, it would depend on your detail scenario. The Dynamics 365 Commerce provide more powerful comprehensive omnichannel commerce across e-Commerce, in-store, and call center than PowerApps Portal. But the cost you spent in Dynamics 365 Commerce would be higher than PowerApps Portal.
More details about Dynamics 365 Commerce, please check the following article:
https://docs.microsoft.com/en-us/dynamics365/commerce/commerce-architecture
Best regards,