I don't usually like to interject, but a quick moment, please.
The first passage you referenced was metaphorical. Do you really think we will need gold and silver in eternity? This is a reference to the testing of faith, as in 1 Peter, where it is refined and proven of value by trials and whatever perseverance is demonstrated through them. Even if a son of God doesn't make top marks, a son will not lose his inheritance.
This passage doesn't speak of an inheritance.
1 Corinthians 3:10-15 YLT
10) According to the grace of God that was given to me, as a wise master-builder, a foundation I have laid, and another doth build on it ,
11) for other foundation no one is able to lay except that which is laid, which is Jesus the Christ;
12) and if any one doth build upon this foundation gold, silver, precious stones, wood, hay, straw—
13) of each the work shall become manifest, for the day shall declare it , because in fire it is revealed, and the work of each, what kind it is, the fire shall prove;
14) if of any one the work doth remain that he built on it , a wage he shall receive;
15) if of any the work is burned up, he shall suffer loss; and himself shall be saved, but so as through fire.
There is no mention of inheritance, rather of either reward or loss.
Our works are here described as being tested by fire, and compares the gold, and the silver, and the precious stones as building materials, the same with the wood, and the hay, and the stubble, all building materials.
The context, both before and after this part, concerns created division in the body of Christ. So the point here is, you are either building with the right stuff, or with the wrong stuff.
In my interpretation, this is to say you are either building up the body of Christ in love, such as described in Ephesians 4, or you are "building" with such as comes from one's self, and not the Holy Spirit.
I agree with you that the reward is not money. Some places speak of crowns, such as where Paul tells the Thessalonians that they are his crown of rejoicing when they will be in the Lord's presence. The reward is how joyful we will be when we see those to whom we have ministered in the glory of the Lord.
Daniel wrote that those who are wise will shine like the brightness of the sky, and those who turn many to righteousness as the stars of heaven forever.
I don't know that we really can conceive of exactly how it will be.
This is not a passage of the testing of faith as Peter describes, this is a judgment at the end our our lives.
1 Corinthians 3:13-15 YLT
13) of each the work shall become manifest, for the day shall declare it , because in fire it is revealed, and the work of each, what kind it is, the fire shall prove;
14) if of any one the work doth remain that he built on it , a wage he shall receive;
15) if of any the work is burned up, he shall suffer loss; and himself shall be saved, but so as through fire.
This is God's judgment of the results of our activity in this life.
On the other hand,
1 Peter 1:7 LITV
7) so that
the proving of your faith, much more precious than perishing gold, but having been proved through fire, may be found to praise and honor and glory at the revelation of Jesus Christ;
This is not about works, rather, that our faith be shown genuine as we endure the fiery trial.
The second passage does not apply as you attempt. Fitness for the kingdom? This passage is about how the Spirit works. Did you choose when you were born? So do you think you get to choose when you're born again?
The passage speaks for itself, no comment needed.
John 3:3-7 LITV
3) Jesus answered and said to him, Truly, truly, I say to you,
If one is not generated from above, he is not able to see the kingdom of God.
4) Nicodemus said to Him, How is a man able to be generated, being old? He is not able to enter into his mother's womb a second time and be born?
5) Jesus answered, Truly, truly, I say to you,
If one is not generated out of water and Spirit, he is not able to enter into the kingdom of God.
6) That having been generated out of the flesh is flesh, and that having been generated out of the Spirit is spirit.
7) Do not wonder because I said to you, You must be generated from above.
Much love!