Hello Nikolai,
You can hide the product fields from Sellacious Backend > Settings > Global Configuration > Backend Display Options.
As to hide the Pricing Tab from Seller's profile, you can handle seller's permissions from Sellacious Backend > Settings > Permissions. Select seller and in denied the permission for
Edit Own Pricing.
As for hiding the payment method, I do not want to show it to the client, since it is only one. This will facilitate the perception of the order form by the Client.
Currently, checkout without payment is not supported. We can custom it for you. However, you can disable the checkout and in pricing, you can use Query form as an order form.
I hope this helps.