Love the cover art! Overall, this is a very cute little submission and I love the idea of going on adventures with your cat. Composition wise, the second part of your four part chord progression with the higher piano parts sounds a bit off to me. It's in key, but using different notes in the scale on that bar I think would have delivered a sound that fit the rest of the song more appropriately.
The feedback you've gotten around velocity and volume is on point, I think. As someone who learned music by messing around with straight MIDI in Noteworthy Composer, it definitely took me a long time to "figure out" velocity - especially when you talk about using higher quality soundfonts or samples that actually reflect the subtle changes in tone of a real instrument. The piano is the most important example of this - the tone shift from playing a note softly to banging on the keys is incredibly dramatic and can really make your piano sound "flat" or "dead" or "fake" if you don't account for it properly.
Practice makes perfect though - just keep experimenting and playing around with different velocities as you write new melodies and you will begin to understand what works better. Looking forward to seeing how you've progressed in future jams!