Ima ukupno dva pakovanja.

Here ima is an impersonal existential form, so it means there is / there are, not he/she/it has.

So:

• Ima ukupno dva pakovanja. = There are two packages in total.

Serbian often uses ima this way when talking about existence, quantity, or availability.

Because Serbian does not need a dummy subject like English there.

English says:

• There are two packages.

Serbian simply says:

• Ima dva pakovanja.

So the idea of there are is built into the construction with ima.

Ukupno means in total, altogether, or all together in the sense of total number.

It tells you that the number being given is the final total.

You can think of the sentence as:

• Ima dva pakovanja. = There are two packages.
• Ima ukupno dva pakovanja. = There are two packages in total.

Because pakovanje is a neuter noun.

In Serbian:

• dva is used with masculine and neuter nouns
• dve is used with feminine nouns

Examples:

• dva stola = two tables (sto is masculine)
• dva pakovanja = two packages (pakovanje is neuter)
• dve knjige = two books (knjiga is feminine)

A good clue is that pakovanje ends in -e / -nje, which is typical for neuter nouns.

After dva, tri, and četiri, Serbian uses a special counting form of the noun.

So you get:

• jedno pakovanje = one package
• dva pakovanja = two packages
• tri pakovanja = three packages
• četiri pakovanja = four packages

So dva pakovanje is incorrect.

With pakovanje, the correct form after dva is pakovanja.

In meaning, it is clearly plural, because it refers to two packages.

Grammatically, after dva/tri/četiri, Serbian uses a special numeral construction. With pakovanje, the form pakovanja happens to look the same as some other forms as well, which can be confusing to learners.

The important practical point is:

• after dva, say dva pakovanja

Yes. Serbian word order is fairly flexible.

All of these are possible:

• Ima ukupno dva pakovanja.
• Ukupno ima dva pakovanja.
• Ima dva pakovanja ukupno.

They all mean roughly the same thing, but the focus changes slightly.

• Ima ukupno dva pakovanja. sounds neutral and natural.
• Ukupno ima dva pakovanja. puts a little more emphasis on the total.
• Ima dva pakovanja ukupno. is also possible, with ukupno added at the end for emphasis.

Yes, it is possible, but it sounds more formal or abstract.

• Ima ukupno dva pakovanja. = the most natural everyday way
• Postoje ukupno dva pakovanja. = more like there exist two packages in total

For ordinary counting or stating availability, ima is usually the better choice.

With pakovanje, you would say:

• jedno pakovanje = one package
• dva pakovanja = two packages
• tri pakovanja = three packages
• četiri pakovanja = four packages
• pet pakovanja = five packages

So a full sentence could be:

• Ima jedno pakovanje.
• Ima tri pakovanja.
• Ima pet pakovanja.

With this particular noun, the form pakovanja appears with several numbers, so the number word itself is what tells you how many there are.