Mi ne metas sukeron en mian teon, ĉar mielo estas sufiĉe dolĉa por mi.

Because Esperanto often uses the present tense for a general habit or something that is usually true.
So Mi ne metas sukeron en mian teon means something like I don't put sugar in my tea in general.

If you wanted a one-time past action, you would use metis.
If you meant the future, you would use metos.

The -n marks the direct object. In this sentence, sukeron is the thing being put somewhere.

• Mi metas sukeron = I put sugar
• sukeron is what receives the action of metas

Even though sugar is a mass noun in English, in Esperanto it still takes -n when it is the direct object.

Because in Esperanto, some prepositions can be followed by -n to show direction or movement toward a place.

Here, the sugar is being put into the tea, so en mian teon shows movement into my tea.

Compare:

• en mia teo = in my tea / inside my tea, location
• en mian teon = into my tea, direction

So the tea is the destination of the sugar.

Because adjectives in Esperanto agree with the nouns they describe in number and case.

So:

• teo = tea
• teon = tea as a direct object or directional form
• mia = my
• mian = my, matching teon

Since teon has -n, mian must also have -n.

In Esperanto, ne usually comes right before the word or part of the sentence that it negates. Here it negates the verb:

• Mi ne metas = I do not put

That is the normal and most straightforward placement.

Ĉar means because and introduces a full clause:

• ĉar mielo estas sufiĉe dolĉa por mi
  = because honey is sweet enough for me

Pro means because of / due to, and it is followed by a noun phrase, not a full clause.

So:

• ĉar mi estas laca = because I am tired
• pro laceco = because of tiredness

In this sentence, since the reason is expressed as a whole clause, ĉar is the correct choice.

Sufiĉe is an adverb meaning enough or sufficiently. It modifies the adjective dolĉa:

• sufiĉe dolĉa = sweet enough / sufficiently sweet

If you said sufiĉa, that would be an adjective meaning sufficient. That is a different structure.

So:

• mielo estas sufiĉe dolĉa = honey is sweet enough
• mielo estas sufiĉa = honey is sufficient

The sentence wants to talk specifically about the degree of sweetness, so sufiĉe dolĉa is the natural form.

Because dolĉa is a predicate adjective after estas. It describes the subject mielo.

• mielo estas dolĉa = honey is sweet

It is not:

• dolĉe, because that would be an adverb meaning sweetly
• dolĉan, because there is no direct object here

So dolĉa is the correct form.

Por mi means for me or to my taste / for my needs.

It makes the statement personal:

• mielo estas sufiĉe dolĉa por mi
  = honey is sweet enough for me

Without por mi, the sentence would sound more absolute, as if honey were simply sweet enough in general.
With por mi, it clearly means according to my preference.

Esperanto does not use an indefinite article like a/an, and la is only used when definiteness needs to be marked.

A few reasons la is absent here:

• mian teon already has a possessive, so my tea is definite without needing la
• sukeron and mielo are being used as general substances, so no article is needed

So this is completely natural Esperanto.

The letter ĉ is pronounced like ch in church.

So:

• ĉar sounds roughly like char
• sufiĉe sounds roughly like soo-FEE-che

A few helpful details:

• c = ts
• ĉ = ch
• stress in Esperanto is always on the second-to-last syllable

So:

• SU-fi-ĉe
• ĉAR

Yes, Esperanto word order is fairly flexible, but this version is the most neutral and natural.

For example, the reason clause could move:

• Ĉar mielo estas sufiĉe dolĉa por mi, mi ne metas sukeron en mian teon.

That means the same thing.
Still, the original sentence is a very standard way to say it.