Normally, in conditional type 2 that indicates an unreal or imaginary situation, you use the past tense in the if-clause, and would + infinitive in the main clause. For example:
If he did this, it would be easy for him.
But, sometimes, you also use the subjunctive would + infinitive in the if-clause to show willingness to do something on the part of the subject of the if-clause.
If he would do this, it would be easy for him.
The speaker of the sentence implies that he is not willing to this, so it won't be easy for him.
The second sentence in the conditional type 3 should be formed as follows:
If he had done this, it would have been easy for him.
As for the third sentence, it's completely incorrect; you don't use -ing form immediately after the modal would.
Regarding the sentence 'If he had done this, it would be going to be easy for him', it's correct grammatically. It is a mixed type 3 and type 2 conditional. It implies that he didn't do this, so it's not going to be easy for him.