Hey thanks Jon! 
You're right, I think I played the left hand too loud. I tried to play it softer and it already sounds quite different. Any tips on good tone production? coz sometimes when I play softly the sound tends to disappear :p
The rule of thumb I go by is that someone shouldn't be aware of anything other than the melody, but if they are listening for something other than the melody, they'll hear it distinctly. In other words, play it as loudly as you want as long as it doesn't disturb the melody.
Phrasing sounds quite advanced though. I notice that it also involves how to vary the speed that a passage is played, am I right?
Yes, tempo has a bit to do with phrasing. Unfortunately, it's hard to describe phrasing without letting you hear the choices. My general approach to phrasing is to listen to others play the song while I'm learning it myself, and when I have it fully memorized or at least have it so that I don't have to focus on reading the music that much, I then try to focus on the melody and bring it out. I do it subconsciously -- I don't actually concentrate on it, I just listen to myself playing it. If something doesn't strike you as good, make a mental note to try it again.
Practicing a song over and over, trying different crescendos and decrescendos, will result in you having your own interpretation of the song because through that trial and error, you will have settled on what you think is the way it should be heard.
Any recommendation on which Chopin preludes are suitable for beginners like me?
Hmm.. I think Prelude in E Minor should be ok. After that perhaps Prelude in B Minor. I suggest these two because they don't require extraordinary fingering techniques, but present the challenge of bringing out a melody over a repeated note. In the first, the right hand has the melody while the lefthand has repeated chords that change. It's really quite beautiful. The second has the melody being the left hand with repeated notes in the right hand. If you can master these two songs, you'll have what you need down for phrasing

Both of those preludes can be found on my site (although I didn't work them up fully, someone wanted to hear them, so I recorded them hastily) at
https://jon.maccoding.com/music/. Both are recorded on a keyboard that was really hard to try to put expression and dynamics into, but I think you can still hear what I'm talking about here. (I plan on upgrading my keyboard in the next few weeks, so maybe I'll re-record them on it when I get it)
Sorry if I ask too many questions... 
One can't ask too many questions

Plus, I hope to start teaching lessons once I buy myself a house, so it helps for me to try to answer questions like these
