No me gusta usar mucha colonia cuando hace calor.

Because gustar works differently from the English verb to like.

In Spanish, gustar is closer to to be pleasing to. So:

• Me gusta usar mucha colonia literally means Using a lot of cologne is pleasing to me
• me = to me
• gusta = is pleasing

So Spanish does not say I like X in the same way English does. It says something more like X pleases me.

Yo gusto is usually not what you want here. It would mean something like I am pleasing / attractive, depending on context.

No makes the sentence negative.

• Me gusta usar mucha colonia = I like using a lot of cologne
• No me gusta usar mucha colonia = I do not like using a lot of cologne

In Spanish, no normally goes directly before the conjugated verb:

• No me gusta...
• No quiero...
• No hace calor

Because the thing being liked is the action to use / using.

After gustar, Spanish often uses an infinitive when you like or do not like doing something:

• Me gusta leer = I like reading
• No me gusta correr = I do not like running
• No me gusta usar mucha colonia = I do not like using a lot of cologne

So here usar is not conjugated because it is functioning like using in English.

Because the subject of gustar here is the whole action usar mucha colonia.

A whole infinitive phrase counts as singular, so you use gusta:

• Me gusta nadar
• Me gusta viajar
• Me gusta usar mucha colonia

You use gustan when the thing pleasing someone is plural:

• Me gustan los libros
• Me gustan las flores

In this sentence, the subject is not many colognes. It is the single idea/action using a lot of cologne, so gusta is correct.

Because colonia is a feminine singular noun, so mucho has to agree with it.

Agreement:

• masculine singular: mucho
• feminine singular: mucha
• masculine plural: muchos
• feminine plural: muchas

So:

• mucha colonia
• mucho perfume (because perfume is masculine)
• muchas flores

This is standard adjective/determiner agreement in Spanish.

In Spain, colonia commonly means cologne or a scented fragrance, often lighter than perfume.

Depending on context, it can refer to:

• cologne
• fragrance
• scented body splash

It does not mean colony here, even though the word looks similar in English.

In everyday Spanish from Spain, colonia is a very normal word for personal fragrance.

Hace calor is the standard Spanish expression for it’s hot or the weather is hot.

Literally, hace comes from hacer and looks like it makes heat, but you should learn hace calor as a fixed weather expression.

Common related expressions:

• hace calor = it’s hot
• hace frío = it’s cold
• hace sol = it’s sunny
• hace viento = it’s windy

So in cuando hace calor, the meaning is when it’s hot.

Not in this context.

Está caliente usually means that a specific thing is physically hot:

• La sopa está caliente = The soup is hot
• El café está caliente = The coffee is hot

For weather, Spanish normally uses:

• hace calor = it’s hot

So:

• cuando hace calor = when the weather is hot

Using está caliente for the weather would sound unnatural or just wrong in most normal situations.

Because it expresses a general situation: whenever it is hot or when it’s hot.

Spanish often uses the present tense for habitual or general truths:

• Cuando llueve, no salgo = When it rains, I do not go out
• Cuando hace frío, llevo abrigo = When it’s cold, I wear a coat

Here, cuando hace calor means something like:

• when it’s hot
• whenever it’s hot
• in hot weather

It is not tied to one specific moment unless the context makes it specific.

Yes. The meaning stays basically the same.

You can say:

• No me gusta usar mucha colonia cuando hace calor.
• Cuando hace calor, no me gusta usar mucha colonia.

The second version puts more emphasis on the condition when it’s hot.

Both are natural.

You could, but the meaning changes slightly.

• No me gusta usar mucha colonia... = I do not like using a lot of cologne...
• No me gusta mucha colonia... = I do not like a lot of cologne...

The version with usar clearly focuses on the action of wearing/using it. Without usar, the sentence sounds more like you dislike the presence or amount of cologne itself.

So the original sentence is better if you want to talk about your own habit of applying fragrance.

By itself, mucha colonia means a lot of cologne. It does not automatically mean too much, although context can suggest that idea.

So:

• neutral/basic meaning: a lot of cologne
• possible implied meaning in context: more than I want to use

If you want to be more explicit about too much, Spanish might say:

• demasiada colonia = too much cologne

So the sentence as written is softer and more natural than a stronger statement with demasiada.

Yes, depending on the nuance.

Possible alternatives:

• llevar = to wear
• ponerse = to put on

Examples:

• No me gusta llevar mucha colonia cuando hace calor.
• No me gusta ponerme mucha colonia cuando hace calor.

Differences:

• usar = general, very natural
• llevar = focuses on wearing it
• ponerse = focuses on applying it to yourself

The original usar is broad and completely correct.