Sorry to hear about all the difficulties you are having.
As Matilda correctly says, don't be too disheartened if your MR is not successful, remember, this is just the DWP looking again at their OWN decision, they are not likely to change it unless you attach some fairly compelling evidence that they have not already seen - this does not necessarily mean that you would not be successful at appeal!
My advice would be to submit the MR, keeping it fairly brief - details of the decision you are appealing (PIP, date of decisions), brief details of your conditions and how they affect you, and then a brief explanation of why you disagree with the decision. There's no need to go further than about a page unless you really want to (in which case go for it!).
I view the MR almost as an administrative step that must be taken in order to get an appealable decision.
I would recommend trying to get a local CAB, welfare rights, or money advice worker to help with the appeal - they may not be able to assist with the MR, but I'd try asking.
Hope this helps!
Let us know if you need anything further