Hello Ashraf,

1. Yes, you can use the free version of sellacious for your published site. However, there'll sellacious branding at the bottom of every sellacious page. You can remove this branding whenever you want by subscribing to community or cloud premium plans.

https://www.sellacious.com/pricing
https://www.sellacious.com/sellacious-cloud-marketplace-pricing-annual

2. To use any payment method in the checkout, integration with sellacious is mandatory. If you want, we can integrate this for you. You can know more about integration here,

https://www.sellacious.com/hire-us

3. Below is the link for sellacious payment plugin documentation.

https://www.sellacious.com/documentation-v2#/learn/payment-methods/developer-documentation

I hope this helps.

Thank You