Safely charging jump-start battery with 80W solar panel?
1) Voltage. As long as the voltage is within spec, the jump starter will draw as much current as it wants, not more. If the voltage goes over spec, all bets are off.

2) In principle, yes.

3) Not a problem, will only draw what it needs (as long as voltage is ok).

4) Superfluous amps don't matter. They're simply not used.