How do you build a structured sales process for a digital agency that works with Enterprise Ecommerce Clients?

I own a small growing digital eCommerce agency based in Philadelphia. I'm searching for a mentor to help develop our sales process, as we are growing and running into issues due to not having a clearly defined sales process when it comes to starting a new relationship with a client. We work with Magento & Shopify Plus. We have mainly worked on small projects the last several years, but our goal has always been to go big or go home. We are running into the following issues in our sales process: - Initial contact with large clients generating between $20-200m in revenue we don't have a good process dealing with these size clients. We are trying to figure out how to put it all together so we can gather requirements in a structured process while being considerate of our time. - Understanding what resources to bring into the sales process and when. Example: We have a client who needs a full eCommerce implementation with complex customizations and integrations, but then they also need marketing services. We don't have a process of when and how we bring in other resources to discuss their needs. Our biggest problem is having a process and structure because it might come off to a client that we are unorganized, but the real issue is we haven't figured out how to put it all together. - How to estimate on phases accurately? We currently do it by hours, but we've been advised to do it by days.