I'm sure others will have better answers, but the simple one is that you have to create a Custom Form based on the object type. If you want a form for Requests then it has to be created as an Issue-type Custom Form. Then, if you plan to turn that Request/Issue into a Project you have to duplicate that same exact form with the same exact fields into a Project-type Custom Form – it acts as a receptacle form to "catch" all the data entered by the requester as it transfers the data from an Issue into a Project.