The "original" eternal form of the marginal living entity (jiva-soul) is a "two arm" form like Krishna (that the human species also have).

Only when the jiva soul chooses to enter the Vaikuntha Planets does the four armed form manifest that is similar to the four armed Vishnu form. 

The marginal living entity or jiva soul's body is made up of -

Sat - eternity 

Chit - knowledge 

Ananda - bliss

Vigraha - bodily form

Devotee - “Is the original body of the spirit soul a human form?”

Srila Prabhupada - “Yes, human form. God is also human form. “Man is made after the shape of God.” So God is also like human form. Here you see Krsna, two hands, two legs”. (Srimad-Bhagavatam Canto 6 Chapter 1 Text 1-4 Melbourne, May 20, 1975)

The "original" eternal form of the jiva-soul is NOT some impersonal formless spark in the Brahmajyoti or Brahman as the impersonalists and Mayavadis believe. 

Srila Prabhupāda - "We are spark so long it does not develop a body. But because it is spirit, it cannot remain in that impersonal stage. He wants to enjoy. So, so long he has forgotten, he develops a body which is called matter".

Śyāmasundara - "Does the jiva soul develop a spiritual body? One or the other?"

Srila Prabhupāda - "No. He is spirit, spiritual identity already. But as we are developing material body, similarly we can develop spiritual body".

Revatīnandana - "You very clearly explained to me once in a letter that if the spirit soul then goes into the brahmajyoti, he is considered still fallen. Still fallen. Does that means the whole brahmajyoti is composed of fallen souls? You see my question? If I go there, I'm a jīva soul, and I go to the brahmajyoti I'm still fallen".

Srila Prabhupāda - "Yes".

Revatīnandana - "That means all jīva souls there are also fallen souls".

Srila Prabhupāda - "Yes".(Room Conversation August 17, 1971, London)

Srila Prabhupada - ''Existence in the impersonal brahman is also within the category of non-Krsna consciousness. Those who are in the brahman effulgence are also in the fallen condition, so there is no question of falling down from a fallen condition. (Letter to: Revatinandana, Los Angeles 13 June, 1970) 

Srila Prabhupada - ''When fall takes place, it means falling down from the non-fallen condition. The non-fallen condition is Krsna consciousness'' (Letter to: Revatinandana, Los Angeles 13 June, 1970)

The "original" form of the jiva-soul has "two arms" like Krishna and their "original" home is Goloka-Vrindavana.

Therefore only when the jiva-soul "chooses" to leave Goloka Vrindavana and enter the Vaikuntha Planets, do they manifest their four armed form like Lord Vishnu or Lord Narayana. 

There are billions of different perpetual Vaikuntha Planets that take up 3/4 of the Spiritual Sky, each having their own Vishnu form with their own unique name that describes the pastimes on their Vaikuntha planet.

Vishnu/Narayana forms are all expansion of Krishna via Krishna's first expansion, His brother Balarama.

There are also three other major Vishnu expansions that build and manage the material temporary creation which is 1/4 of the Spiritual Sky.

1 - Maha Vishnu who creates ALL the massive Brahmanda universes that originate from the pores and breathing of His Body.

2 - Garbhodakashayi Vishnu who enters deep inside each Brahmanda universe and creates a secondary smaller universe where Brahma further creates many planetary systems (14 in our universe)

3 - Paramatma (who accompanies each individual jiva-soul that enters the material creation)