My name is Maria, I am a sales manager. I will be glad to answer your questions.
Different payment plans are not included by default. However, it's possile to set commissons per each vendor (% or a flat rate).
Speaking about promotions, as featured products, vendors, etc. will be blocks that can be created by the root admin only, it's possible to sell them to vendors. In case you would like vendors to purchase them through the platform, some modifications will be needed.
Various modifications are possible, because Multi-Vendor has the 100% open access to the source code.
Please, feel free to contact us at firstname.lastname@example.org, we will be glad to discuss your project in more detail and provide all the necessary information.