Website migration to new host(Modx, FTP, without Cpanel connection)

We want to migrate our company website on a new hosting service. What we have: 1) Website is using Modx. 2) We can connect to the site files through an FTP connection. 3) We can connet to a modx content management system. 4) Website files that you can download. We'll provide the downloadable link. 5) We have the access to the domain name. We can make the necessary forwarding to the new host. What we don't have: 1) We don't know what kind of a server runs the web site. (linux or windows, apache, php or etc ?) 2) We don't have access to a control panel(like cpanel or plesk). Requirements: 1) To run the website on a demo host and show us the website is working fully functional. 2) Demo host will be provided and managed by you. 3) You may recommend a reliable hosting service with necessary services included so that the website can work. And we will buy the service and provide the account to you to migrate the site to this hosting. 4) Until we see the demo site is fully operational, we will not make a payment or prepayment. We make the %50 payment through freelancer when we see the demo is working. %50 will be payed after the succesfull migration to the real host. 5) You might need to deal with compatibility issues because the website has been designed 5 years ago. You shall take all necessary actions to make it work. (As the site working now, it can work when you migrate it, so this shouldn't be an actual problem)