Thank you, bro, for praising me.

In very informal writing, such as a SMS/text message, the commas are often omitted.

I have a clear goal, which is to master English (or: to learn English very well), so I have to stick to it.

When you “master” English, you learn it very well. We don’t say we “master English well” because “well” would be redundant.

Thank you for offering this amazing WeChat group for us, and it(or: to) us, which seems to benefit everyone.

Thanks to the people here who have good English, thatI am gives men theis chance to learn.

Two different ways of saying pretty much the same thing:
"Thanks to the people here who have good English, I am given this chance to learn."
“I thank the people here who have good English for giving me the chance to learn.”

Thank you bro for praising me.

Alternative: Thanks for your kind words.

Thank you for offering this amazing WeChat group forto us, and it seems to benefit everyone.

Alternative: Thanks for creating this amazing WeChat group for us, it looks like everyone can benefit.

Thanks to people here who have good English, that gives me the chancehelping with their good English, I have new opportunities to learn.

I am grateful to all of you, my dear and respectful group members.

As tofor speaking, I will achieve it within one or two years.

As for someone/something is a fixed expression: https://www.ldoceonline.com/dictionary/as-for-somebody-something

Thanks to people here who have good English, that gives me the chance to learn.

This sentence doesn't sound very natural to me, as it is not clear if you are thankful to the people, or thankful for the fact that their English is good. You could say something like 'thanks to the people here who have good English and are giving me the chance to learn' (however this could potentially sound insulting as it implies there are people in the group who do not have good English!)

I am grateful to all of you, my dear and respectful group members.

This not not incorrect but I just wanted to clarify "respectful group members" = the group members act in a respectful manner / "respected group members" = a formal way of say you have respect for the other group members