Hi onestep,
The UC Migration process is supposed not to leave you worse off. But UC is paid in different phases to the Benefits it's replacing so there is an approximate 5 week wait from the start of the UC claim until payment date.
If you find yourself being unable to manage financially you can apply through your UC online account ( or on a smart phone ) for an Advance.
As far as rent and the change from Housing Benefit to UC Housing Costs I have recently been in touch with a large social landlord as part of my other job as a local Benefits adviser. I have been told that their staff have been trained in what to expect from Managed Migration. So I think it is best for you to contact your social landlord directly to get the best advice.
David
Nothing on this board constitutes legal advice - always consult a professional about specific problems 
