No. Jesus does not uphold literally
all things by his word. The context is in regards to what God made
through Jesus in these last days. This would be the church/Messianic age. According to Hebrews 1:1,2.
As head of the church, Jesus does indeed serve God in the functional capacity as Lord of the church, shepherd, high priest, and mediator between mankind and God Himself, but is not God. In this sense, Jesus upholds all things [in the church] with his word.
I believe you are misunderstanding what it means for the fullness of God's deity to dwell in someone. It isn't something unique to Jesus, as Paul said.
Eph. 3
19of the love of Christ, and to know this love that surpasses knowledge, that
you may be filled with all the fullness of God.
The firstborn of many brothers. Therefore, he himself isn't God. The best possibly analogy for the relationship between God, Jesus, and the church was already provided by the Bible. It's Father (God) and God's children such as Jesus and the church who are not themselves God.
Romans 8
29For those God foreknew, He also predestined to be conformed to the image of His Son, so that He would be the
firstborn among many brothers.
What's that?
Amen. Scripture plainly states this. It is not a problem when one understands that Jesus is not himself God.
I am not sure what you think this passage from 1 John 1 means, but the disciples were not there at the literal beginning (of creation) to see, hear, or touch anything. They are referring to the beginning of the ministry of Jesus, the beginning of the church age, the beginning of the preaching and miracles. Jesus got all of the doctrines from God, not himself, and went around doing good and healing
after God was with him. (Acts 10:37,38)