I’m thinking about buying some assets off the marketplace. If i do what are the limits on them?. am i allowed to use them to sell in my game if i get to that point. Do i need to credit the seller?. What do i need to do to use these in a commercial project.
There is a terms of use text you should read, but I cannot find the link right now.
Short summary: You can use it as you want commercially as long as the product is a packaged experience, that is you cannot resell the content for use as assets in another persons game. No credit needed.
"All content sold on the Marketplace is licensed to the buyer (who may be either an individual or company) for the lifetime right to use the content in developing an unlimited number of products and in shipping those products. The buyer is also licensed to make the content available to employees and contractors for the sole purpose of contributing to products controlled by the buyer.
Each such product built using content purchased on the Marketplace must be a standalone creative work (such a game, simulation, or video) in which content is merely a component and not the primary focus. For example, it may not be a content pack for distribution to engine users"
Here you can read more about it: https://www.unrealengine/marketplace/marketplace-business-terms-faq 
Thanks for the link and the help everyone.