Am I buying too many different units?

https://preview.redd.it/bq01w8fyt5yd1.png?width=2066&format=png&auto=webp&s=869f75a2ffba8c7b90a565d0b49b86ef19b64241

So after watching some YT and getting some chaff basics down I rose quite rapidly from 250 to 500+ MMR. Now I feel like I have a new scenario that comes up more often. See pic.

I won first 6 rounds or so, but then I just get overwhelmed late game. Am I buying too much things spreading my upgrades thin? I feel like my early has improved a ton but I just lose the armsrace more often now.

Also, when is it appropriate to level up a unit?