Analysing hands - Learning EV calculation

I know this a lot of queations but the help would be invaluable and grealty appreciated.

Is this the key to improving as a player?

I would like to learn the EV calculation. How do you use when analysing a hand overall?

Is it something that can only be used when you are trying to push a person off a hand?

Is it for all in only?

Can you use when calling?

Does anyone have some good examples?

Can you use it for the following example?

Live tournement
Blinds 100/200

Stacks
Mid 10800 (Tight ABC approach)
Button Hero 11600 (Learning semi aggressive (7,8s)
SB 4500 (Tight)
BB Villain12700 (Aggressive, raises a lot)

Play
Mid limps
Button limps (Would quite often raise in this spot but has done it a on a few occasions before)
SB - Limp
Pot - 800
BB raises 800
POT 1600
Mid folds
BU calls 600
SB Folds
POT 2200

What types of things need to be considered?
1. Range .....villain maybe top 40% of hands
2. Pot size
3. Type of players
4. Odds and implied odds - BU can paid off big if good flop

In you opinion is this a bad play?

What would be the EV calculation for this example?

Is this a good example of how position can be of an advantage?Button has postion and can fold without to much damage to stack.

Incidently............
FLOP 7, 4, 2
Villain makes continuation bet 1400
POT 3600
HERO reraises 3300 total
POT 6900
Villain folds