If the mould is only on the surface, then do as the "expert" said and use bleach to clear it - assuming that the backboard is of a formica, melamine or other non-porus facing material.
(To check for surface mould, simly wipe a small patch with the bleach, and if it comes away 'clean' then bleach is all that's needed. If after cleaning the patch, a fair bit of the mould is ingrained in the surface, then you will have to tell us what the backboard is made out of before a definitive answer can be given).
Make a hole in the ceiling by all means, but simply to let any water residue out - forget spraying the wood 'just in case fry rot sets in'.
If the leak is cured and there is plenty of ventilation in the roof space - then you won't get dry rot (it's by far the wrong conditions for this type of rot).
As for the rest of what the 'expert' says, then from the small amount of information given, he's right and *NOT* cutting corners and doing the amount of work that will cause the least damage and inconvenience - and cost to you or your insurance company.
Cash