I believe in triune God even if the word Trinity is not in the bible. Just because the exact word is not there doesn't automatically means the concept is wrong. What matters is that the "principle" is there.
Consider Matthew 3:16-17 "16 When He had been baptized, Jesus came up immediately from the water; and behold, the heavens were opened to Him, and He[a] saw the Spirit of God (Holy Spirit) descending like a dove and alighting upon Him. 17 And suddenly a voice came from heaven , saying, “This is My beloved Son, in whom I am well pleased.”
This is where God the Father, The Son (Jesus) and The Holy Spirit are clearly present in one occasion.
And also Jesus commanded to baptize in their names, Matthew 28:19 "Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit."
There are distinctions(in nature and in functions) yet all three has an attribute of God. And the bible also says there is only one God. How did this happen? we don't know as it was not directly revealed to us but I believe it by faith. But is this possible? Of course, nothing is impossible with God.
Did Jesus Christ remained as a spirit only? No, after His resurrection He is with a glorified body as well. Just as the believers will have glorified body in our resurrection. I personally believe our image and likeness are in accordance to Jesus Christ. That is why we are being transformed into His image, Romans 8:29 "For whom He foreknew, He also predestined to be conformed to the image of His Son ..."
Man is a triune being. Spirit(from God), Body(from earth), and Soul(out of the Spirit and Body). Genesis 2:7 says "And the Lord God formed man of the dust of the ground (BODY), and breathed into his nostrils the breath of life (SPIRIT); and man became a living being (SOUL). I believe our soul is triune as well having MIND, WILL and EMOTION.