I’d like to make a liberal comment with this observation. Having read most of the threads lately and this one is among them, there is a prevailing trend in which learners are posting long lists of questions and dialogs asking for correction help. Making correction for this kind of thread is much more time consuming and challenging because of the many problems the helpers encountered in this kind of posts with either the tone, logic, structure and grammar, or all of the above.
Since all your “B” dialogs are pretty much identical, I will comment on the “A’s”.
A: What do you do? “what do you do?” without additional context simply means ” what kind of work do you do?”. But when you add: (when you have free time) (on your spare time) then it will sound more coherent with the B dialog. Otherwise, the question is irrelevant.
B: I practise English almost all the time.
A: That sounds like a real ball. I think you must have improved your English so much.
“real ball” seems to be misused with the practice context.
A: You can answer all the questions in this way.
B: That sounds like a great idea.
A: Do you want to play Digimon with me? (Digimon is the name of a computer game.) When you invite someone, “would” is the choice word. I wouldn’t say it is wrong to use “do” however.
B: That sounds like a lot of fun. I like the game very much.
A: Do you want to go to for a movie with me tonight? Same with the above.
B: That sounds great/ nice. However, I am tired out today. The tone is quite stiff. However – is much too formal in a casual conversational context. A casual reply: “That’s sounds good, but I think I may have to take a rain check. I am really pooped / tired today”.
A: You can download all kinds of things with Xunlei.
B: That sounds nice/great.