Do I need an IV to use AES-CTR as a CSPRNG? I'm using AES128-CTR for generating pseudo-random values, which is considered secure for up to 1MB (at least from what I've read).

I simply encrypt a 128-bit little-endian counter, starting from 0.

Should I use an IV? Should I start counting from a non-zero random value? Does it make any practical difference?
When using counter mode you can start at any value, it doesn't matter.  The only important thing is that you never use the same counter value twice for the lifetime of the key.  So, as long as your key is actually random and, as you say, you don't use it for more than 1 MB of data, then your generator should be fine.