If i get a Multi IFR rating, would that mean I have a single IFR and multi rating? or do I have to get all 3 ratings separately?

If you do your IFR ride (flight test or IPC) in a single engine aircraft, you get a group 3 (single engine) instrument rating. If you do it in a mult engine aircraft, you get a group 1 (multi engine + single engine) instrument rating.
However, you have to be able to fly a multi-engine aircraft (passed the requirements for a multi engine rating / flight test, or have the multi engine rating) to be able to do the group 1 IFR ride. Some examiners may be willing to do both rides at the same time (either in the same flight or back-to-back).