"1-3" is between pins 1 and 3.
What they don't indicate is whether flux is peak or peak-to-peak. I would assume it's peak, and so we use the calculation:
$$ \Phi_\text{pk} = \frac{V}{4 F_\text{sw}} $$
In push-pull configuration, that's 10V across the ends (1-3), or 8.3µWb.
Minimum probably refers to the minimum limit. A random part might handle more, but they're guaranteed to handle this.
The limit is saturation flux density in the core. But they don't give core specs and turns count, so we only get the in-circuit or terminal flux limit instead.
Saturation can be measured, and therefore statistics on production parts could be compiled. More likely the limit is the calculated design limit, rather than statistically.
Voltage is essentially unlimited, as triple-insulated wire is used. The voltage rating extends over the full length of both windings. But given the low flux rating, you'd have to raise frequency an extreme amount to even get close to stressing the insulation, and core losses melt the thing long before then.
Core loss is not rated, presumably because of the intended application. Use it at 5V 300kHz with the suggested SN6501 style driver and you're fine.
(Also, V.s ≡ Wb (weber) if you're curious, and, I don't know why they're using siemens (S), but alas it's a common typo not using lowercase s (seconds).)