"Hey" - just thought it is too casual in the whole context. Put your customer's name, or even a simple "Hi" is better than "Hey"
"no matter what vendor you will select at the end..." - I would prefer " no matter which/what vendor you select in the end..."
"The same question went back to Cisco 10 years ago" - I would prefer " the same question goes back to ..."
"... and so many lesson learnt when rolling out..." - I would prefer " and many lessons were learnt when..."
"End users are very much less forgiven if ..." - It should be " End users are much less forgiving if..."
"How soon can the system recovery from .." - I think you meant " recovers"
"... the dependancies have to addressed up front.. " - it should be " have to be addressed up front..."
"... on some of those points in our quick call.. " - I would prefer " ... in a quick call..."
"no matter what vendor you will select at the end..." - I would prefer " no matter which/what vendor you select in the end..."
"The same question went back to Cisco 10 years ago" - I would prefer " the same question goes back to ..."
"... and so many lesson learnt when rolling out..." - I would prefer " and many lessons were learnt when..."
"End users are very much less forgiven if ..." - It should be " End users are much less forgiving if..."
"How soon can the system recovery from .." - I think you meant " recovers"
"... the dependancies have to addressed up front.. " - it should be " have to be addressed up front..."
"... on some of those points in our quick call.. " - I would prefer " ... in a quick call..."