HI,
you can easily use only FM-BCS parrt only we just implement same at my place . you need not to change material ledger from FAGLFLEXT to FMGLFLEXT.
you can transport request on 31,mar and go-live from next day. when you port request to production server same time you have to keep ready budget against commitment items because system will ask budget on every where after transporting. so better to prepare budget ready and lock the user till budget upload.