Go back to first principles:

For the discrete case, EV can be calculated using:

EV[X] = x1*p(x1) + x2*p(x2) + ... + xn*p(xn)

where:

x(1,2,...,n) = possible outcomes of X
p(x1,x2,...,xn) = probability of each outcome occuring

Consider your flop lead in limped pot:

Villain limps with a range of [A] and you check behind with range (or perceived range depending on what level your opponent is thinking on) [B].

The pot is 2BB going into the flop and comes down [F].

You want to know the EV of leading 1.5BB here with a perceived leading range of [C]?

To calculate the EV of leading this flop:

EV(lead) = f*2 + (1-f)*EV(not fold)

The fold equity (FE) you have is easily calculated:

FE = f*2

where f = % time villain folds

f is a function of a number of variables:

- How much equity does [A] have vs [C] on [F]?
- How much equity does [C] have vs [A] on [F]?
- How does villain react to flop leads in limped pots with:
- His hands that "hit the flop?
- His hands that "missed" the flop?

Your calculation assumes you have 0 equity when villain doesn't fold. "50% of time I lose my bet"

This is generally not the case.

Against your flop lead villain can [fold, call, raise, jam].

To calculate your EV, you need to estimate which hands he will take each of these actions with and calculate your equity against each of these ranges.

You end up with a decision tree incorporating all future actions, their payoffs and their associated probabilities. This would theoretically include all [actions,reactions] on all future streets.

It would look something like:

EV(lead) = f*2 + (1-f)[EV(lead,call)+EV(lead,raise)+EV(lead,jam)]

This requires a lot of assumptions about the hands in each of these segments of villain's range and practically becomes somewhat useless without reads to justify the assumptions you make.

In reality, most people calculate the results of discrete single street games to estimate the EV of a particular action.

For example, you may take the view:
- Villain limps a weak range [A]
- [A] usually misses [F]
- Villain plays fit or fold vs flop leads in limped pots
- I will bet out 1.5BB to pick up the dead money and give up if he doesn't fold.
- This will be profitable (EV > 0) if:

EV = f*2 - (1-f)*1.5
f > 1.5/3.5
f > 43%

So under these assumptions, if villain folds more that 43% of the time, your play will be +EV.

But it's not necessarily the most +EV play.

Note: I'm not going to try to address your turn and whole hand EV calcs because I think you would be better taking a different approach.

Picking arbitrary % on the turn will not help you make better plays at the tables.

Realise that you are now on the turn, conditional on previous streets play:
- Preflop went limp-check
- You lead out 0.75P and villain calls

Every time you bet, you affect villains range of hands on subsequent streets.

Going back to fundamentals: why are you betting?

- Value (can you be called by worse hands)?
- Bluff (can you make villain fold his equity share of the pot by betting)?

Reading your post I think you would benefit a lot from thinking about your decisions having first considered

- villain's range (+ tendencies)
- your perceived range (+ table image)

within the context of the:
- board texture
- effective stack depth
- gameflow.