Сперва я открываю письмо, а потом уже отвечаю.

In Russian, the present tense can be used to describe:

• a habitual action: This is what I usually do
• a step-by-step description: First I do X, then I do Y

So Сперва я открываю письмо, а потом уже отвечаю can sound like:

• First I open the letter, and only then do I reply
• What I do first is open the letter, and then I answer

It does not have to mean only right now, at this very moment.

If you wanted a one-time future meaning, Russian would usually use perfective future forms, for example:

• Сперва я открою письмо, а потом отвечу.

If you wanted a past meaning:

• Сперва я открыл письмо, а потом ответил.

This is mainly about aspect and tense.

Открываю is:

• imperfective
• present tense

That makes it good for:

• repeated/habitual actions
• describing a general sequence
• focusing on the process or pattern rather than one completed event

Compare:

• открываю = I open / I am opening / I usually open
• открою = I will open once, completed
• открыл = I opened once, completed

In this sentence, the speaker is describing the order of actions as a general pattern, so открываю fits naturally.

Yes, in many situations you can use either сперва or сначала to mean first / at first / first of all.

So these are both natural:

• Сперва я открываю письмо...
• Сначала я открываю письмо...

The difference is mostly stylistic:

• сначала is usually more common and neutral
• сперва can sound a little more literary, conversational, or stylistically marked depending on context

For a learner, it is safe to treat them as near-synonyms in sentences like this.

Both а and и can connect parts of a sentence, but they do different jobs.

Here а works well because it marks a kind of contrast or progression between two stages:

• first I open the letter,
• and then / whereas after that I reply

It helps separate the two steps more clearly.

If you said и потом, it would sound more like simple addition:

• and then

That is possible in some contexts, but а потом is very common when contrasting one stage with the next.

So in this sentence, а потом feels very natural.

Great question. In this sentence, уже does not mean literal already in the simple time sense.

In а потом уже отвечаю, уже adds the idea of:

• only then
• not before that
• after that step is done

So the meaning is something like:

• First I open the letter, and only then do I reply.

It gives a nuance of sequence and completion:

• first the opening happens,
• then the replying happens as the next proper step

Without уже, the sentence is still correct:

• Сперва я открываю письмо, а потом отвечаю.

But уже makes the order feel more definite and slightly emphatic.

Письмо is the direct object of открываю, so it is in the accusative case.

However, for neuter inanimate nouns, the accusative singular is often the same as the nominative singular.

So:

• nominative: письмо
• accusative: письмо

That is why the form does not change.

Compare with a feminine noun, where you would see a visible change:

• Я открываю книгу.
  • книга → книгу

In Russian, отвечать / ответить can often be used without stating the object if it is obvious from context.

Here the context is письмо, so отвечаю naturally means something like:

• I reply
• I answer it
• I respond to the letter

Russian often leaves out things that are understood.

You could make it more explicit in different ways, depending on the exact meaning:

• отвечаю на письмо = I reply to the letter
• отвечаю ему = I answer him / reply to him

But in the original sentence, omitting the object is normal and natural.

Yes. Письмо can mean:

• a traditional paper letter
• an email/message in many contexts

Modern Russian often uses письмо for email too, especially when the context makes it clear.

So this sentence could mean:

• First I open the letter, then I reply
• First I open the email, then I reply

Yes, я could be omitted if the subject is clear from context.

Russian often drops subject pronouns because the verb ending already shows the person:

• открываю = I open
• отвечаю = I reply

So you could say:

• Сперва открываю письмо, а потом уже отвечаю.

That sounds natural too.

Including я can do things like:

• make the sentence a little clearer
• add mild emphasis
• sound slightly more explicit

So both versions are possible.

Russian word order is flexible, though not random. The original sentence is very natural:

• Сперва я открываю письмо, а потом уже отвечаю.

But other versions are possible, with slightly different emphasis:

• Я сперва открываю письмо, а потом уже отвечаю.
  • a bit more emphasis on I
• Письмо я сперва открываю, а потом уже отвечаю.
  • more emphasis on the letter
• А потом уже отвечаю at the end keeps the focus on the second step

The original order is good because it clearly presents the sequence:

1. сперва
2. а потом уже

Yes. Отвечаю comes from отвечать, which is imperfective.

So both main verbs here are imperfective:

• открываю ← открывать
• отвечаю ← отвечать

That fits the idea of a general routine or habitual sequence.

If you wanted to describe a single completed future sequence, you would normally use perfective verbs:

• Сперва я открою письмо, а потом уже отвечу.

If you wanted a single completed past sequence:

• Сперва я открыл письмо, а потом уже ответил.

Not exactly. Открываю specifically means open, not read.

So the Russian sentence literally refers to opening the letter/email first.

If you wanted read, you would use читаю:

• Сперва я читаю письмо, а потом уже отвечаю.
  • First I read the letter, and only then do I reply.

So открываю and читаю are different stages:

• open
• read

Even though in real life opening an email often implies reading it, the verb itself still means open.

This is an aspect pair:

• отвечать = imperfective
• ответить = perfective

Very roughly:

• отвечать focuses on the process, repetition, or general action of replying
• ответить focuses on one completed reply

Examples:

• Я отвечаю на письма каждый день.
  • I answer letters every day.
• Я уже ответил на письмо.
  • I have already replied to the letter.

In your sentence, отвечаю fits because the speaker is describing a general sequence or usual procedure, not one finished reply event.