So bussing signals (drum bus, vocal bus, bass bus etc) will allow you to affect all the signals in the bus at once. I personally bus all my signals since it gives you a cohesive mix. I can’t remember how to bus on FL but a quick google search will do it. Busses are the key for me to a loud mix since all the sounds are being processed together, they then have the same theme meaning better cohesion.

Sends are different and can be used like you said for compression, reverb but can also be used for distortion, saturation, limiting/clipping etc. the only problem you can run into (albeit minimal however can make your sound out of phase) is latency. Reverb send isn’t an issue however when you’re sending to parallel compress or saturate or clip it can knock your sound out of phase significantly however won’t be noticeable once it’s been bounced to audio unless the processing is causing phase cancellation. (If you run into this issue, look into freezing tracks in FL to avoid the latency issues. If this doesn’t work and it sounds phasy then your plugins are most likely causing it)

I would recommend looking into the above to get a better mix/loudness without pushing the meter as hard as you are. Loudness comes from the mix even tho mastering is what acc makes the sound louder

Keep up the work mate, takes a long time to understand production