The best advice is RENT,RENT,RENT.
This is very expensive gear and you want to know beyond a shadow of a doubt that this is what will make you happy.
There are real differences from your 35mm gear. Cleaning the sensor is not a major attraction to MF IMO.
While you will see a jump in IQ you may be surprised how it compares to properly prepped 35DSLR files.
There has been some discussion above about the ability to do extreme tilts and shifts in MF. While this is possible with a technical camera and a MF back, it is not true for the Hasselblad and Mamiya bodies. Further, if you do use a technical camera you will be working very slowly and will be applying correction layers to compensate for the unusual color shifts and falloff peculiar to the backs on tech cameras.
The real risk IMO is if you buy, you will be itching to upgrade in few years when they bring out the new sensors. Granted it is just the back but it is still real money.
If you are a pro you will need a spare back and a spare body.
So renting may be a better option than EVER owning.