Hi,
All open items (including PR/PO) should be generated in FM. You have to foresee budget for this. You can distinguish it (if you have business requirement for this) for other budget by assignment to a different FM object (fund, commitment item, etc.). Creation of FM documents after PSM-FM implementation is done via FMCN/FMCT transactions. You can find plenty of material about these transactions on SCN.
Regards,
Eli