What are instances, in the Old Testament, that reveal what sort of God He is, particularly in His great love, mercy, & solicitude toward man?

Genesis 3:15, for one.

"His great love, mercy, & solicitude toward man"? You obviously haven't read the Old Testament. Start with Genesis 6:7 " So the Lord said, “I will wipe from the face of the earth the human race I have created—and with them the animals, the birds and the creatures that move along the ground—for I regret that I have made them.”

Wiping the Earth clean of all life apart from one family and their floating menagerie does not show "love, mercy, & solicitude toward man".

And spared not the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world of the ungodly

2 Peter 2:5

13 And God said unto Noah, The end of all flesh is come before me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.

Genesis 6:13

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And I saw heaven opened, and behold a white horse; and he that sat upon him was called Faithful and True, and in righteousness he doth judge and make war.

Revelation 19:11

but with righteousness He will judge the poor, and with equity He will decide in favor of the earth's oppressed. He will strike the earth with the rod of His mouth and slay the wicked with the breath of His lips.

Isaiah 11:4

And the heavens shall declare his righteousness: for God is judge himself. Selah.

Psalm 50:6

https://images.knowing-jesus.com/w/700/01-GENESIS/...