It is hardly possible to be authoritative on the symbolism of Revelation, but these are the connections which I traced in my own book;
The premise (my own guess) that one of the factors in the original concept of the "four living things" in Ezekiel and Revelation was the idea that they represented the "four winds", notionally associated with God's throne in the clouds.
God's threat to scatter Elam by unleashing upon them "the four winds from the four corners of heaven". (Jeremiah ch49 v30, RSV)
In Zechariah ch6, the judgemental forces of God against the world are pictured as four chariots, pulled by horses of different colours.
In Revelation ch6, the judgemental forces of God against the world are pictured as four horses of different colours.
In Revelation ch7 v1, four angels are holding back "the four winds of heaven" to prevent them blowing on the earth. In v2, another angel orders them not to harm the earth, sea, or trees. That order is given aloud so that we may know what's happening. The other angels are obeying it already; holding back the [destructive] winds has the effect of delaying the campaign of harm to the earth, postponing it to the next chapter.
In fact what is happening in ch7 v1 is the suspension of the "four horses" campaign of ch6. That is why the martyrs were told they would have to wait before their vindication could be completed (ch6 v11). In other words, the "four horses" and the "four winds of heaven" are two different images for the same judgemental process.
If the four living creatures represent the four winds, and the four horsemen represent "the four winds of heaven" in judgement mode, then that is the connection between them.
The seven bowls are the climax of the judgemental process.