would in future tense

Hello everyone!
it is my first time to write a question down here.
Nowadays, I'm struggling with understanding a modal verb 'would'

The word "would" is said to be conditional verb, and we use this word such as "We're going by train. If we went by bus, it would be cheaper, but train is quicker." And I think this sentence contain the meaning that "we don't expect we will go there by train, but I guess~~"
And, also, we use this word this way without using "if clause" like

Jason:"It would be nice to buy a new car, but we can't afford it."

Anderson: Shall I tell Chris what happened?
Harry: I wouldn't say anything
(=I wouldn't say anything in your situation)

I guess those sentence contain "imagination which is not real" just like that sentence above. That is, Jason doesn't have intention to buy a new car because buying a new car is not affordable to him. And even though Harry said "I wouldn't say anything", he didn't expect he would be in Anderson's situation. Rather, he told Anderson an advice. In addition, because those usages are similar to usages of would with If-past form, it seems that we can add if-past form before or after these sentences.

Jason: "If I had a lot of money", it would be nice to buy a new car. but we can't afford it.

Anderson: Shall I tell Chris what happened?
Harry: "If I were in your situation", I wouldn't say anything.

I think these sentences are natural as well, and with such activity, I inferred that If the word "would" is used in present tense, it means (Of course! it might not same as the meaning) "I guess I will~~ (but reality is different)" Applying my assumption to those sentences

Jason:I guess It will be nice to buy a new car. but we can't afford it<- it indicate impossibility

Anderson: Shall I tell Chris what happened?
Harry: I guess I won't say anything.

there might be a little degree differences, but I guess they are almost same.
And, in this way, I was able to understand another modal verb "would have p.p." So following two sentences

"I would call Lisa, but I don't have her number."

and

"I would have called Lisa, but I didn't have her number"

have only difference of time tense but no meaning difference, I guess. And with my assumption, at last, I was able to plenty of tricky usage of "would". but I found exceptions and these exceptions are used in future tense.

1. I'm not going to invite them to the party, They wouldn't come anyway.
2. You should go and see the film. you would enjoy it.
3. Why don't you go and see Clare? she would be very pleased to see you.

I think these would usages are different. Also, it seems to me that we even can exchange these "would" to may/might or will and meanings are same. And different to what I said before, these sentences don't contain the meaning of "unreality" or "impossibility."
Because this things made me quite awkward, I made my own assumptions.

If the word "would" is used in future tense, because nothing hasn't happened yet, It can mean only "pure guess" and it lead to similarity to may/might or will in future tense.

I remember (but not sure) my teacher taught me "would" can be used in future tense, and it is similar to "will" but degree of certainty is different. she said "will means 100% certain in speaker's thought, but would is not." but, isn't related to conditional or unreality like that? and what's difference between would and may/might or will in future tense?

Thank you for reading this loooooooong question. I will wait for your answer