“If you believe in an afterlife,
is your dead-and-gone-to-heaven form fully human? Or is it a spiritual thing?”
No, we will receive “glorified bodies” that are incorruptible and free of infirmity:
“20 For our conversation is in heaven; from whence also we look for the Saviour, the Lord Jesus Christ:
21 Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself.” Philippians 3:20-21
“if Jesus was human/divine while he walked the earth, did he remain fully human after the resurrection?”
He appears to have remained in his earthly form at least until he was assumed to heaven, because the disciples saw his wounds. However, we know that when he returns to earth, it will be in his glorified form (Mark 13:26,1 John 3:2), and we got a preview of that form during the Transfiguration:
“17 And after six days Jesus taketh with him Peter, and James, and John his brother, and bringeth them up into a high mountain apart:
2 and he was transfigured before them; and his face did shine as the sun, and his garments became white as the light.” Matthew 17:1-2
This glorified form also seems to be depicted in the description of the “rider on a white horse” from Revelation 19:11-16:
“11 Then I saw heaven opened, and behold, a white horse! The one sitting on it is called Faithful and True, and in righteousness he judges and makes war. 12 His eyes are like a flame of fire, and on his head are many diadems, and he has a name written that no one knows but himself. 13 He is clothed in a robe dipped in[a] blood, and the name by which he is called is The Word of God. 14 And the armies of heaven, arrayed in fine linen, white and pure, were following him on white horses. 15 From his mouth comes a sharp sword with which to strike down the nations, and he will rule them with a rod of iron. He will tread the winepress of the fury of the wrath of God the Almighty. 16 On his robe and on his thigh he has a name written, King of kings and Lord of lords.”
Thank you for your response.
So Jesus was, but is not now, simultaneously fully God and fully man.
Hence it is not heresy to say so.