Enhance#1 - Require to copy forms from existing process to another process

This is not currently available in Forms. You can copy the process to effectively copy the forms, then rebuild the process to whatever you're looking for. If you have an existing process, you could copy the original process to duplicate the forms, then copy the other process and paste it in. The hard part about copying forms from one process to another is getting the variable mapping right. We have heard this feature request before, but it has not been scheduled for a release at this time. I'll add your comment to the request ticket. 

Enhance#2 - Require to copy field rules from the existing form and paste it into another form

Similar to the above, if you copy the whole process, it will copy the forms and field rules as well. Once you have those copied, you can modify the process. Field rules are all based on the field IDs in the form, if you tried to copy a field rule from one form to another, it wouldn't know which fields to show/hide based on which conditions on the new form. 

Enhance#3 - Require to take new variables at every step

I'm not sure what this means. You don't need to make new variables at each step of the process. On your first form you can drag fields on to create variables. On the second form, instead of dragging new fields, go to the variables tab in the form designer and drag on existing variables. If a value is entered on the first form, the second form will load with that value. 

Enhance#4 - Require multiple grouping in the report section

This is not currently supported, but it is a feature request we've heard before. I'll add your comment to the request ticket.