In 1 Corinthians 4, Paul calls himself and Apollos “stewards” who have been entrusted with the most important thing imaginable, the “mysteries of God.” Like a fund manager, he is to protect God’s investment but also work to ensure a return on God’s investment.

No.
But as Gordon Fee points out, God seeks stewards who are faithful. They are not chosen due to their “not eloquence, nor wisdom (nor ‘initiative,’ nor ‘success’—our standard requirements).” Those who have been entrusted with the Gospel are to humbly servant the master and seek his glory and honor alone. The leaders of the Corinthian church are failing in just this regard, they are seeking their own honor rather than the one who has called them.
Paul and Apollos have been entrusted with the mysteries of God (4:1-2). A steward in this context is a servant entrusted with a task, a commission. Paul uses a slightly different word for servant in 4:1 than in 3:5 (ὑπηρέτης vs. διάκονος), but there is likely no difference in meaning. In both cases the servant is subordinate to a master and serves by doing the will of that master.
A steward (οἰκονόμος) is a manager or administrator. This could be a servant put in charge of a household (Joseph, for example, or the servants in Jesus parable in Luke 16). It can refer to a city official, such as a public treasurer, the word used to describe Erastus in Rom 16:23. An administrator is charged with a task (manage a city’s money, for example). In the LXX, the word translates Hebrew words of civil administrators (1 Kings 4:6, 16:9, Isa 36:3, 22, 37:2, etc., cf., eight occurrences in Josephus with the same sense).
The content of this deposit is the “mysteries of God.” Rather than a huge sum of money to invest and protect, Paul is a servant of God’s revelation. Mystery is typically something that must be revealed to be known, a secret hidden until the time is right. This is not something guess-able, but rather a revelation of something new and previous unknown.
In order to be a successful steward, they must be “found faithful.” If the steward is a money manager for a city, they have to protect the money entrusted to them and invest it in a way that returns a profit. Paul and Apollos are therefore accountable for their management of the mysteries of God. The preaching of the Gospel will naturally expand the body of Christ, and there are some strategies Paul might use to preach the Gospel in ways that are more likely to bear fruit. He goes first to the synagogue, for example, since that is where he will find people who already know the Scripture and may be looking forward to the coming of the Messiah, as well as some God-Fearing Gentiles who are interested in the Jewish God. When he was in Athens, he went to Mars Hill, a place where people enjoy discussing new ideas and debating philosophy. His goal was to go to the location where he would have the best chance getting an audience for the Gospel.
If Paul describes Apollos and himself as servants and stewards, then certainly the leaders of the church at Corinth are servants as well! Verse 6a Paul says that the things he has applied to himself and Apollos are applicable to all Christian leaders at every level, from a nursery worker to the long-time elder to the Lead pastor.
For Paul, the right attitude of a Church leader should be: “This is God’s church and I am just taking care of this for a while.”
What are some specific ways this servant-attitude can transform how the local church does ministry?