A very sweet question.
In Vrndavana, we eternally serve Radha Krsna in a specific group or camp, as per our serving capacity. That is why Vraja Bhakti is known as Raganuga Bhakti. Raganuga Bhakti means that which follows in the footsteps of the Ragatmikas (the eternally liberated like Radharani, Baladeva etc).
When we enter in Vraja, we enter into a specific group under a specific leader to serve Radha Krsna. For example, if you are in Sakhya rasa ( mood of friendship with Krsna) the you will serve under one of the 12 cowherd friends of Krsna Balarama. If you are in Vatsalya rasa (parental mood), you will serve the Lord as one of the friends of Yashoda maa. Madhurya rasa is little complicated. There are first primary Sakhis like Radha, Candravali etc, and you may serve under them as a Gopi. Under Radharani there are 8 Sakhis (headed by Lalita, Vishaka etc) and each of these 8 Sakhis have 8 manjaris and each of these 8 manajaris have 8 and so on. I will give you an example.
Kamala Manjari, who is eternally dear to Lord Radha Krsna, serves under Her praneshwari Ananga Manjari. In turn Ananga Manjari (who is the leader of the Manjaris in Radhakund) serves Rupa Manjari, who in turn serves Lalita who finally serves Radha and Krsna. In Vraja there are millions and billions (a great deal) of souls who serve but each soul is content in their Seva and they always have a chance to directly serve Radha Krsna. The amazing thing is, the manjaris get even more happiness then Radha and Krna themselves. See, the pleasure that Krsna gets from interaction with His devotees, Radharani gets an even higher bliss. And the Manjaris experience a bliss even higher then Radha and Krsna. This is known as Parampara. As the mercy descends it becomes greater and greater.
That being said, every soul has a chance to serve and see Radha Krsna. In Vraja even the dust spec is concious and are able to see at every moment what Radha and Krishna are doing. The Lord is so merciful that He personally accepts the service of each and every devotee.
Now you asked the question, why does the Lord expand in so many forms and perform pastimes with Himself.
The reply is this. Rasa or divine nectar is the essence of all existence. The highest Truth is not simply eternity or consciousness, but bliss. In order to taste higher and higher limits of Bliss and allow His devotees to do the Same, Lord Krsna expands in forms. For Bhakti there must be two never one, so that is why the Sumpreme Truth splits into Radha and Krsna in order to enjoy these pastimes. Just like we jivas desire to enjoy and have fun (this is our innate desire) this desire is also found in Ishwara who also desires to enjoy with His devotees. In such interactions, both Bhagavan and His devotees are pleased as they reach higher and higher limits of ecstasy. That is why the Upanishads say raso vai sah (He Brahman is embodiment of rasa).
The Jivas are simply manifestions of the Lords Jiva Shakti. They are eternal, and their sole purpose is the engage in devotional service to the Lord. The Lord is the only enjoyer, while we are the enjoyed. The jivas are also eternally distinct from God, because they are minute while God is massive. God possesses all spiritual qualities in full, but Jivas only have them in tiny quantity. It is possible for the Jivas to merge with God, but that is inferior to Bhakti, because it is only Bhakti which can satisfy them. Just like the perfection of an instrument lies its proper use, the perfection of the Jivas lies in sweet Bhakti to Lord Hari. Another thing to note, is the pastimes happening in Vraja/Vaikuntha are eternal. Lakshmi Devi always existed, Balarama Ji always existed. There was never a time when they did not exist, the concept can be quite mindboggling actually. Trying to apply our intellect to the sweet pastimes of Lord Hari will leave our intellect in pieces.
Tldr: bliss is the highest principle and for this reason Goloka is the way it is. Goloka is eternal, and never a created, as so the Jivas.
