Hi Sachin,
You can create all the buttons that you need, the buttons are defined in customizing, if you want to create a button to create a sales order take function EHSWA_141_WASTEMVT_CRT_MM_PO in function group EHSWA_141 as a reference, your function must have the same signature.
The sales order must be also considered as a follow-on document
A follow-on document is a document linked qith the entry document.
In your case create the follow-on document for the sales order, then you must create first and Application fuction, later assign this application function to the Document category.
Regards.
JCD