yàobù míngtiān chī huǒguō? hǎozhǔyi!

Here, 要不 means something like How about... ?, Why don't we... ?, or What if we... ?

In this sentence, 要不明天吃火锅？ is a casual way to make a suggestion.

A very useful thing to know is that 要不 can have another meaning in other contexts: otherwise / if not. So its meaning depends on the sentence.

In this line, it is clearly the making-a-suggestion use.

No, they are different.

• 要不 = How about... ? / Otherwise...
• 要不要 = Do you want to... ? / Want or not want?

For example:

• 要不明天吃火锅？ = How about eating hotpot tomorrow?
• 明天要不要吃火锅？ = Do you want to eat hotpot tomorrow?

The second one asks more directly about someone’s preference. The first one sounds more like a suggestion.

Chinese often leaves out the subject when it is obvious from context.

In 要不明天吃火锅？, the implied subject is usually 我们 or 咱们:

• 要不我们明天吃火锅？
• 要不咱们明天吃火锅？

But in natural conversation, Chinese speakers often omit it because everyone already knows who is being talked about.

This is very common in Mandarin.

Because time words in Chinese usually come before the verb phrase.

So the basic order is often:

[subject] + [time] + [verb] + [object]

Example:

• 我们明天吃火锅。 = We will eat hotpot tomorrow.

In your sentence:

• 要不 + 明天 + 吃火锅？

That follows the normal pattern.
Putting 明天 before 吃火锅 sounds natural and standard.

In Chinese, 吃火锅 is the normal expression.

• 吃 = eat
• 火锅 = hotpot

Even though hotpot is also a kind of dining experience, Mandarin commonly uses 吃 for many food-related activities, just like:

• 吃饭 = eat a meal
• 吃烧烤 = eat barbecue
• 吃饺子 = eat dumplings

So 吃火锅 is simply the standard way to say eat/have hotpot.

Yes, definitely.

• 吃火锅 = eat/have hotpot
• 去吃火锅 = go eat hotpot / go have hotpot

Adding 去 emphasizes the idea of going somewhere to do it.

So these are both natural:

• 要不明天吃火锅？
• 要不明天去吃火锅？

The version without 去 is a little shorter and more general. The version with 去 makes the outing feel more explicit.

Because not all questions in Chinese use 吗.

This sentence is a suggestion question, and suggestions are often made with intonation and a question mark alone.

• 要不明天吃火锅？

That already sounds like How about eating hotpot tomorrow?

If you added 吗, it would usually sound less natural here.
So for this kind of casual suggestion, no 吗 is normal.

Literally:

• 好 = good
• 主意 = idea

So 好主意！ means Good idea!

Chinese often drops 是 in short exclamations like this.
A fuller sentence would be:

• 这是个好主意。 = This is a good idea.
• 真是个好主意！ = That’s really a good idea!

But in conversation, just saying 好主意！ is completely natural.

Because 好主意 is the normal way to say good idea.

When 好 directly describes a noun in a simple, common expression, Chinese often does not need 的.

So:

• 好主意 = natural
• 好的主意 = possible in some contexts, but less natural here

In an exclamation like Good idea!, the standard choice is definitely 好主意！

It is pronounced zhǔyi, and the last syllable yi is usually in a neutral tone.

So:

• 好主意 = hǎo zhǔ yi

Learners often want to pronounce 意 with a full fourth tone, but in this word it is normally light and unstressed.

That is why the pinyin is often written as hǎozhǔyi.

No. 要不 is very flexible and can be used for many kinds of suggestions.

For example:

• 要不我们坐地铁？
  How about we take the subway?

• 要不你先回家？
  How about you go home first?

• 要不今天别去了？
  How about not going today?

So in your sentence it happens to be about hotpot, but the structure works for many situations.

Yes. A few common alternatives are:

• 我们明天吃火锅吧！
  Let’s eat hotpot tomorrow.

• 明天去吃火锅怎么样？
  How about going to eat hotpot tomorrow?

• 咱们明天吃火锅，好吗？
  Let’s eat hotpot tomorrow, okay?

Compared with these, 要不明天吃火锅？ sounds casual, conversational, and slightly tentative, like you are tossing out a suggestion.

Yes. It is a very natural, positive response.

It means the speaker likes the suggestion. Depending on tone of voice, it can sound:

• friendly
• approving
• enthusiastic

Other similar responses could be:

• 不错！ = Not bad!
• 可以啊！ = Sounds good!
• 行！ = Okay!/Sure!

But 好主意！ specifically means That’s a good idea!