Olton Pete - the key phrase you use mate is "if all the dashes are available"
60-61 aircraft might be all that is needed, but is that allowing for maintenance, or even more likely how much tech cover is required?
Several airframes have left the fleet now (running at about 51 dash and 14 ejets I think) so allowing for 2 or 3 on maint. It doesn't take much disruption before you run out of options.
Flybe are also making themselves available for third party work (like Titan etc), there is also talk (just talk at the moment) that they may have to wetlease airframes to cover shortfalls.
On one day last week 6 dashes were tech, so there isn't much slack, even if it is winter!
Latest guess at 175's arriving, all by month end - possibly, maybe!
As usual Pete, your observations are pretty spot on mate.