PIP back payment effect on other benefits

I'm having my PIP assessment in a few weeks. I'm currently getting ESA support group and Universal Credit LCWRA. I understand that PIP does not count as income and it should not have an impact on UC payments.  However, if PIP awarded, due to the several months passed since my application I'm expecting a huge amount of back payment. If I need to go for MR or tribunal, that's several thousands  of pounds appearing in my bank account overnight. What if I go beyond the £16.000 savings threshold because of this back payment? I would like to use PIP on an electric wheelchair and other expensive things that I can't afford without PIP, but would getting PIP mean I'll lose my other benefits?