How I have spawning working right now is that there is a spawn rate which goes up throughout the game and every time an enemy spawns it picks one room at random to spawn in, then it picks one spot from the predetermined spawn points in that room to spawn at. So yes it is very random with spawning which can lead to it not being as interesting at the start if you get very unlucky and have a bunch all spawning in the same room, however, at the end it's kinda a non-issue as there are so many spawning that there is almost always at least one in a room. I could try implementing a pattern to see how well it works out though.
Yes, the time showing up like that is a bit annoying, it has to do with how I was making the timer. With a bit more time this can be solved, I just needed that time during the jam to work on more important things. As for the negative hp, I originally had it just go to 0 and not bellow but I really like being able to go to negative numbers; it makes you feel a lot more powerful when you get a critical hit on an enemy and see their hp go to -15.
Also, I just checked out your game and left a comment on it! :)