That's not how forces are calculated. Mass times velocity will be a vector of the dimensions of momentum and mass (of one body) times relative velocity (between the 2 bodies) is a physical quantity I don't know of. Force equals the rate of change of momentum which would be very difficult to calculate here. Even for simple experiments such as two balls colliding, you need to know the coefficient of elasticity, the masses of individual balls, the coefficient of friction between the surfaces etc

Force is literally just mass times acceleration. That's literally Newton's 2nd law.

Your third point is where I'm wrong but it's also not exactly what I was commenting on either. I was commenting on someone saying when two things hit a 300kmh there's a ton of force, which is wrong. And I used the example of bump drafting to shows that. Another example is docking between the LEM and Command Module on Apollo missions. They're both going 35,000 feet/second so when they dock there isn't much force. In this case it looks like the tires hit which causes opposite directions of speed and greatly increases the force of the collision