Yep I agree with "TheBeak", If you get SEIR (single engine) then its only valid on single engine aircraft for IFR, if you do an MEIR (multi-engine) you can fly both SE and ME aircrafts in IFR, if you get the ME rating alone with SEIR then it will be valid for you to fly Multi-Engine in VFR conditions ONLY and single engine Instrument conditions.
I know its pretty expensive but everyone has been through this route, maybe aerodynamics malaga would be a good cheap option for yourself, pretty professional bunch...