Before answering the question, first I want to say this: "Gee, it's nice to hear that PV prices have come down so much that people want to buy more of them up front!"
It used to be that people would budget only part of the PV they need at one, and plan for expansion later.
Anyway....
I expect that charge controllers are reliable enough for the backup to be unnecessary. Furthermore, you can get 60-amp charge controllers (I have a Tri-star TS-60) that will handle your array nicely, and you can choose the controller that fits your budget: The C60's from Xantrex/schneider are cheaper, the Outbacks are more expensive.
You haven't mentioned the battery bank's specs, but that is important in your calculation of value and risk. If the bank is just a jumble of old car batteries, then reliability in the CC's will have no point. If he's bought the latest and greatest Telco system standby battery stacks, then a reliability calculation should be factored in. Also remember that "parallel" systems suffer from increased rates of partial failures. You have replaced one CC with 6 CC's, thereby increasing the chance of failure by 6. The consequence of one failure in the single-CC system is a 100% system failure, while the consequence in a 6-CC system is a reduction in charge capacity by 17%. Sounds good so far, but: During the partial failure your friend may not even notice for a while, maybe a long time, or not until something else goes wrong, and makes him go check on the rest of them.
Trade-offs. Pick the compromise that suits your equipment.
