It depends on the available time you have.
Using the OOTB processes and connector will speed up the development of your processes but it's not as flexible as doing everything by yourself. And once you learned how to use the catalog WebService, and the ServiceDesk webService, you will not want to work with the connector anymore.
To assign an approval you need to use the "assignPendingAction" method, located here : /usm/services/RequestService. This method can be used to assign an approval or an action. You can set the pendingActionType to 1 for an approval and 2 for an action.
Regards,