Here is the situation, I split a sting of electrical plugs to add a junction box to act as the source for an additional sepatarate electrical other plug and a light switch (fo a light).

The box has all whites together (4) blacks together (4) and is grounded properly. 3 of these wires are for the existing line of plugs and new plug and one set is acting as the power source for the light swith. The switch is hooked up the conventional way (both blacks to the switch & whites together & grounded. Is this correct?

Yes

Chuck