Combining multiple VSTs into one output

What is the best way of mixing four input signals to one output signal? By how much should the input signals be attenuated in order to achieve the same theoretical output level as any one input level?

I have tried using logarithmic mathematics but the face that in Cubase there are 3 different ways to adjust the volume of any given VST (why did they have to do this!?!?!) this hasn’t worked out for me.

The following is what I have done so far:

Layered the VSTs into one track per midi controller.

Placed inserts (EQ, Maximizer and Reverb) onto this track (this sounds far better than doing it on a group channel, and is cleaner than doing it the original way: separate VST tracks with separate inserts). To mix the individual VSTs, as some need to be more present than others, I used the “Output Level” or “Level” under the mix tab.
N.B. If I ever need to combine VSTs from different plug-ins then group channeling will be the way forward.

Took the average range (dB) of a reliable sound from my old LIVE project (-18dB to -24dB, this is just how Cubase chooses to divide the ranges on the channel meters).

By adjusting the volume (range: infinity-12dB) on the macro page (homepage) for each VST track I made sure that the Stereo Out volume in the MixConsole screen was at least -24dB but not peaking above -18dB. For complicated sounds this also involved reducing the volume fader in the MixConsole room.

Also there is an interesting forum thread about this topic that I read before posting here about this, sadly they don’t seem to come to a conclusion but thought I’d offer it here too

I have attached screenshots below to illustrate, and hopefully make clearer what it is that I am asking. I don’t work with recordings I purely play live using VSTs as my sound and use keyboard midi controllers.

Thanks in advance!

P.S. I have posted this under the Cubase forum too before thinking this might be a better place, but am not sure.
sound two - screenshot for mixing three signals into one.jpg
sound one - screenshot of mixconsole.jpg
sound one - screenshot for mixing three signals into one.jpg

Here is the fourth, and last screenshot, as I couldn’t attach it to the previous post.
sound two - screenshot of mixconsole.jpg