This weekend, my first collab as a VTuber is going to happen! This weekend, my first collab as a VTuber is going to happen!

sentence is correct - emphasizing "this weekend". If emphasizing that it's your first collab - My first collab as a VTuber is going to happen this weekend! - may be better.

The collab partner isI will be collaborating with 柊優 (Hiiragi Yuu,), who will be the host VTuber. I will be collaborating with 柊優 (Hiiragi Yuu), who will be the host VTuber.

future tense; collab partner is understandable, but a little unnatural.

The collab partner is 柊優 (Hiiragi Yuu,) the host VTuber. The collab partner is 柊優 (Hiiragi Yuu,) the host VTuber.

We wouldn't really say "host VTuber", we would say the collab was going to be on their channel.

The collab partner is 柊優 (Hiiragi Yuu,), the host VTuber. The collab partner is 柊優 (Hiiragi Yuu), the host VTuber.

TheMy collab partner iswill be 柊優 (Hiiragi Yuu,) the host VTuberwho will host. My collab partner will be 柊優 (Hiiragi Yuu,) who will host.

They are my number one favorite streamer. They are my favorite streamer.

number one and favorite sounds redundant

They are my number one favorite streamer. They are my number one favorite streamer.

Use of "they" as a neutral pronoun is controversial. Older people will sometimes require he or she or use "he/she" if the gender is unknown. Younger people are more likely to use "they" as a neutral pronoun or if the gender of the person is unknown.

They are not justNot only are they a streamer, but they are also really big, I mean,popular, as in they have tons of followers on their Twitch and Twitter. Not only are they a streamer, but they are also really popular, as in they have tons of followers on their Twitch and Twitter.

not only...but also; ("a ton" - if more formal)

They are not just a streamer, they are really big, I mean,; they have tons of followers on their Twitch and Twitter. They are not just a streamer, they are really big; they have tons of followers on their Twitch and Twitter.

They are not just a streamer, they are really big, I mean, they have tons of followers on their Twitch and Twitter. They are not just a streamer, they are really big, I mean, they have tons of followers on Twitch and Twitter.

凄いですね！

They are not just any streamer though, they are really big, I mean, t. They have tons of followers on their Twitch and Twitter. They are not just any streamer though, they are really big. They have tons of followers on their Twitch and Twitter.

Also, they are really popular, talented, and kind. Also, they are really popular, talented, and kind.

The collab is about thawill be about Yuu-san and the audience teaching me, (an English Llearner,) English word/s, meme/s, internet slang, etc. The collab will be about Yuu-san and the audience teaching me (an English learner) English words, memes, internet slang, etc.

future tense (this weekend); used parentheses to minimize the use of commas and to not distract from the rest of the sentence; used commas for listing

The collab is about that Yuu-san and the audience teaching me, an English Learner, English words/memes/internet slang, etc. The collab is about Yuu-san and the audience teaching me, an English Learner, English words/memes/internet slang, etc.

The collab is about thathow Yuu-san and the audience teaches me, an English Learner, English words/memes/internet slang, etc. The collab is about how Yuu-san and the audience teaches me, an English Learner, English words/memes/internet slang, etc.

The collab is about thatwill focus on Yuu-san and the audience teaching me, an English Learner, English word/meme/internet slang, etc. The collab will focus on Yuu-san and the audience teaching me, an English Learner, English word/meme/internet slang, etc.

I think that Llanguage learners would enjoy this. I think that language learners would enjoy this.

I think that Llanguage learners would enjoy this. I think that language learners would enjoy this.

I think that Llanguage learners would enjoy this. I think that language learners would enjoy this.

そうですね。

I think that Llanguage learners would enjoy this. I think that language learners would enjoy this.

I am so glad that they suggescontacted me for this collab first. I am so glad that they contacted me for this collab.

The most common phrasing would be that they contacted you for the collab, or that they reached out to you.

I am so glad that they suggested me this collab to me first. I am so glad that they suggested this collab to me first.

I am so glad that they suggested me this collab to me first. I am so glad that they suggested this collab to me first.

I guess I don't have the guts to suggest any collaboration ideas to them. I guess I don't have the guts to suggest any collaboration ideas to them.

"any collab to them" sounds a little awkward

I guess that I don't have the guts to suggest any collab towith them. I guess that I don't have the guts to suggest a collab with them.

I guess I don't have the guts to suggest any collab tos with them. I guess I don't have the guts to suggest any collabs with them.

I guess I doidn't have the guts to suggest any collab to them. I guess I didn't have the guts to suggest a collab to them.

No, it's not about my guts. No, it's not about guts.

No, it's not about mythat I didn't have the guts. No, it's not that I didn't have the guts.

The use of "my guts" in your original sentence is unnatural. Although "have the guts" is a phrase used to describe courage, the word "guts" cannot be used for that meaning elsewhere.