Can you specify what you mean by "custom forms"? Are you talking alternative forms for Page Types or forms from the Forms application (BizForms like Contact Us)?
If Page Type alternative forms, these should be handled automatically. If talking Forms (BizForms), then what Virgil suggested is by far the best route. I'd also suggest cloning the Form webpart and adding some additional checking to ensure that any required fields are available before saving. If you plan to do your own workflow on these forms I'm assuming you'd need to have some type of field(s) that store the state, date and who put the form in workflow. You could also use a global event handler to ensure the fields are added, its up to you.