What happens if the Earth's rotation slows down? Instantaneous stop
I've seen a few posts about what happens if the Earth stopped moving completely. Most seem to assume a scenario in which the Earth stops rapidly. In such scenarios, I have read that there would be tidal waves and extremely fast tornados.
Other posts (such as this one) state there will be no more hurricanes and the climate would obviously be different; with half the Earth overheating. 
More time
At dinner today we got onto the generic discussion of how there "isn't enough time in a day". It was this question which led to me saying we should develop a way to slow down the Earth's rotation. 
A giant parachute
Obviously this isn't a good solution but one I quickly came out with. 
I said that if we could slow the Earth's rotation then we'd have more time in our days. I couldn't see a flaw in this plan. Simply erect a giant parachute (or sail or fin like on a plane) to encounter air resistance ergo slowing the velocity of the Earth. 
There are many flaws to this (naturally), such as the lack of air resistance in space meaning that there won't be any counter acting force to slow the Earth down.
Then the topic of gravity came up. Now I'm no expert when it comes to Physics (I love the idea of it all (but am too stupid) and I watched every episode of The Big Bang Theory), so correct anything that's wrong here. But, my understanding of gravity is that it's to do with mass and velocity. Now, I don't know why I think this or where I'd have heard it but it's what I think. 
All things gravity
I don't really know how gravity works. I understand it that the more mass and high velocity then gravity will be stronger.
Slow, slow, fly off
One of our party stated that if the Earth were to slow down then we'd "fly off" the Earth...
I found this hilarious but it might be true. Here's what I think:
Jump high
I thought that if we slowed down then gravity would be weaker and we'd be able to jump higher!
Finally
All things considered. I'll get to my point. 
Too long, didn't read (tl;dr)
If the Earth's rotation were to slow down, what effects would take place? (By "slow down" I mean if it span at about half the rotations)
Questions


*

*Would the Earth's path around the sun change?

*What would happen to our gravity?

*Would the Earth spinning at half speed mean our days are twice as long?

*A comical question: could we slow down the Earth with some sort of parachute like a dragster has?
4.1. What about adding rockets to make us spin faster? (I'm sorry these are from the point, just find it a funny thought)


My attempts
All my answers to these questions are based on my lack of knowledge of physics. 


*

*Yes. I believe that we'd drift further from the Sun. After that I'm not sure whether we'd maintain a constant path around the sun or just continue away from the Sun. 

*As stated above, I think we'd have weaker gravity. 

*Yes. I feel like this is simple maths. Right? Right?!

*Making it big enough and keeping it within our atmosphere then yeah, I suppose we could.
4.1. As long as we don't go too fast, I don't want a headache.


Disclaimer: I am new here, I'm sorry if I haven't followed the question asking convention.
 A: Here are my answers to your questions:
1)  No, the Earth's path around the sun would not change much.  The Earth's speed of rotation around its own axis does not affect the speed at which it is orbited around the Sun.  A "year" would still be the same amount of time for us, it's just that the days would be longer and there would be less days.
2)  Gravity would also not change noticeably.  Gravity is a force between two objects that depends on two factors only:  Their mass and the distance between the two objects.  In our case, gravity is the attraction between Earth and people.  The speed of rotation of the Earth does not change the mass of Earth or people, nor does it change the distance between people and the center of Earth.
3)  Yes, days would be twice as long.  A "day" is when the Sun shines on a part of the Earth.  "Night" is when the Sun does not shine on the Earth.  The Earth rotating half as fast would mean "day" and "night" would be twice as long.
4)  I doubt you could slow down the Earth's rotation with parachutes.  The thing is, Earth does not rotate through its own atmosphere - it rotates around an imaginary axis in space.  As for adding rockets, I suppose you could cause the Earth to rotate slightly faster, although you would need rockets far more powerful than what we currently have in order to make a negligible difference at all.
A: Some thoughts:


*

*Lengthening days does not necessarily change the duration of our life. It would first of all change the partitioning of our time. So if our days were twice as long, most likely we would only see half of them in total. However, this is a medical question rather than a physics question, and probably the day length has an effect on our life span. I don't know if there are any studies on the subject, but I doubt it.

*The idea of parachutes does not work, because our atmosphere is rotating together with the Earth. See for example the gas giants like Jupiter in our solar system. They consist mainly of gases (call it their atmosphere), and they also rotate. Don't let yourself mislead from the fact that our atmosphere is comparatively thin.

*Rockets could in principle be used to change the rotation speed of the Earth. This would require a vast amount of mass being ejected at very high velocities (at least Earth's escape velocity) away from Earth.

*One minor addition to @Inertial Ignorance's answer: The rotation causes the Earth to be flattened. A slower rotation would slightly change this flattening, resulting in Earth's gravity to change slightly. This would be measurable, but not directly noticeable in everyday life.
