1. What is the maximum landing speed of either plane in Knots, or MPH?
2. What is the maximum approach speed of either plane in Knots, or MPH?
Both will depend primarily on weight, and then airplane configuration. Each type will have a maximum speed for landing flaps, and a maximum tire speed.
What is a typical VNE at 1000 feet altitude,
Around 340kt for the types you have there. It varies with altitude.
how much (if any) can you exceend VNE without stressing the structure of the aircraft?
You'd have to ask the manufacturer, or the pilots who did initial certification testing.
Is an airplane able to fly as fast at sea level as it can at 35,000 feet? If not, how much slower can we expect to fly at sea level?
The indicated speed and mach speed limits will change, but jets will fly faster (TAS) at higher altitudes.