PIP is not means tested but for the purposes of an IVA would be counted as income.
A lot of IVA companies would offset this with higher allowances, given that it recognises that you may have additional needs linked to your disability, but not all companies are that generous.
IVA started March 2011, Completed March 2016 and certificate issued 11 days after final payment. It was not always easy but then some of the best decisions aren't.