First time H1 stamping - Same Client but different employer

I am MS student on H1 after completing OPT now planning for H1 stamping. My Scenario. My vendor worked with consultancy for H1 processing.Client A – Prime Vendor B – Worked on OPT and STEM OPT until H1Client A – Prime Vendor B – Emp C – After H1 start date--------------------------------------------------------------------------------------- Please suggest or answer based on your experience: 1) What is possible answer if VO asks: how come you are working for a longer duration with your client? 2) What is possible answer if VO asks why was an additional layer added with Emp C?3) Will the client and vendor letter be enough or any additional documents are required to prove EVC relationship?4) Is 1 pay check with Emp C enough as I started under Emp C only after H1 approval and do not have more paychecks yet.Thank you.