Good start. I'm a sucker for this type of game. What I have to say is primarily about gameplay, so sorry if I don't answer your questions.
Firstly, I noticed both the enemies and my weapons seemed to make contact without actually touching. There were definitely a few times where a hit was registered when there was still space between.
Secondly, the difficulty curve is a bit steep. In the first level I ended at a point where I didn't even have to move, but the next level I died without killing more than 5 enemies. So maybe a bit of a slighter change would help.
Third, I was able to buy every upgrade after the first level. Maybe the price should go up with each purchase.
Fourth, Junji's starting weapon is a bit hard for a starter. I might suggest changing it.
Like I said, I'm a sucker for this type of game, so I hope to see it get developed more. For weapon suggestions maybe a poison dart, a bamboo spike trap, or a boomerang type weapon could be good