Generally speaking, yes. The normal comparison used is NaCl vs MgO. MgO has about twice the m.p. of NaCl because the electrostatic force of attraction between Mg2+ and O 2- is about double that of the electrostatic force of attraction between Na+ and Cl-, this due to the larger magnitude of charge on the Mg2+ ion and O 2- ion.

Yes. Just take the example of AX vs A2Y, where A+ is a metal ion with a charge of +1, X- is a non-metal ion with a charge of -1 and Y2- is a non-metal ion with a charge of -2. As Y2- has a greater negative charge, it would have a stronger electric field to attract A+ in A2Y than X- would in AX. The same would go for AX vs BX2, where B2+ is a metal ion with a +2 charge. The B-X bond in BX2 would be stronger than the A-X bond in AX. Hence, losing/gaining more electrons would increase ionic bond strength.