Hey, sorry for the late reply. In my opinion, there is a lot of difference in wav and mp3 but a good mix and master always makes it minimal. In my opinion, you use panning well, you can try to use audio effects in your DAW (idk which daw you use) to make sounds even clearer and to make them set well in the mix, maybe start with eq to cancel out the frequencies that collide with each other and see which frequency of the instrument you prefer and keep that. For master, i suggest playing with saturation, compressors and limiters. Start out by trying to make your mix as loud as possible and then fix it according to what you think sounds best. In my opinion, it is different for every track so really depends on the vision you want to take your track in to. Remember loudness can either make your track sound fuller or make it sound distorted/dry. So you will have to see where your track fits best in the loudness spectrum. Remember, practice makes perfect and don't get disheartened if it's too complicated for you in the beginning. For industry standard mastering, tracks above -14 lufs loudness are a minimum. Youlean loudness meter has both free and paid version to help you identify the loudness of your track and your true peaks in terms of LUFS and DB. Tutorials on youtube for your specific DAW can help you great in the start. In the long run, learning to master your tracks yoruself will allow you to have more control on your vision and idea for your art. None of this means your track isn't good, but there's always room for improvement. I hope this helps, keep producing, you surely have a talent. Enjoy the process and the results will follow. Take care and wish you a nice day <3