Мы в основном работаем вместе.

Yes, Russian often drops subject pronouns when the verb ending already shows who is doing the action. Since работаем means we work / we are working, the sentence В основном работаем вместе is possible, especially in conversation.

Including мы makes the subject more explicit. It can:

• add clarity,
• give slight emphasis to we,
• sound a bit more neutral or complete out of context.

So both are possible:

• Мы в основном работаем вместе.
• В основном работаем вместе.

Yes, в основном is a very common fixed expression meaning:

• mainly
• mostly
• for the most part
• basically (in some contexts)

Literally, it comes from в основном = in the main / in the principal thing, but learners should usually treat it as a set adverbial phrase meaning mostly.

Examples:

• Я в основном читаю вечером. — I mostly read in the evening.
• Они в основном дома. — They are mostly at home.

Основном is the prepositional singular form of основной / основное. In the expression в основном, the preposition в is followed by this form.

However, for practical learning, it is best to memorize в основном as one whole phrase, because it functions like an adverb.

So:

• в основном = mostly / mainly

You do not need to analyze it every time you use it.

Работаем is the 1st person plural form of работать (to work).

Conjugation of работать in the present tense:

• я работаю — I work
• ты работаешь — you work
• он/она работает — he/she works
• мы работаем — we work
• вы работаете — you work
• они работают — they work

Because the subject is мы (we), the verb must be работаем.

In Russian, the present tense is commonly used for:

• actions happening now,
• regular habits,
• general facts.

So Мы в основном работаем вместе naturally means something like:

• We mostly work together
• We usually work together
• We tend to work together

This is normal present-tense usage in Russian.

The verb работать is imperfective, and that makes sense because the sentence describes:

• an ongoing activity,
• a repeated habit,
• a general situation.

Perfective verbs in Russian usually do not have a true present tense. They normally refer to a completed future action.

Here the speaker is not talking about one completed instance of working together, but about a general pattern, so the imperfective работаем is exactly what you would expect.

Yes, вместе means together.

In this sentence it tells us how the work happens: the people do the work jointly, not separately.

Examples:

• Мы живём вместе. — We live together.
• Давайте поедем вместе. — Let’s go together.
• Они работают вместе. — They work together.

It is an adverb, so it does not change form here.

Russian word order is flexible, but different orders can sound more natural or place emphasis differently.

The most neutral version here is:

• Мы в основном работаем вместе.

Other possible versions:

• В основном мы работаем вместе. — puts a little more focus on mostly
• Мы работаем вместе в основном. — possible, but less neutral; it can sound like an afterthought or a contrast

So yes, the order can change, but not every version sounds equally natural in every context.

They are similar, but not identical.

• в основном = mostly / mainly / for the most part
• обычно = usually

Compare:

• Мы в основном работаем вместе. — We work together most of the time, though not always.
• Мы обычно работаем вместе. — We usually work together; this focuses more on what is typical.

В основном often suggests that something is true in the majority of cases.
Обычно suggests what normally happens.

Yes, главным образом can also mean mainly / chiefly, and it is close in meaning to в основном.

Compare:

• Мы в основном работаем вместе.
• Мы главным образом работаем вместе.

Both are understandable, but в основном is very common and natural in everyday speech.
Главным образом can sound a bit more formal or bookish in some contexts.

The stress is:

• мы
• в основно́м
• рабо́таем
• вме́сте

So the full sentence is pronounced: Мы в основно́м рабо́таем вме́сте.

This is useful because Russian stress is not always predictable, and getting it right helps both speaking and listening.