Is AES ECB good enough for key spreading?
I then want both to spread the key byte values across the entire key length


Neither is useful. AES is secure without such "spreading" (not a standard term). The method discussed does that fine.

However it is missed a step critical for security of any password-based encryption: key stretching. The idea is to transform the password into the key for AES (as done by the question's method), in a purposely slow manner. This is necessary to avoid a password search attack.

To derive of a key from a password you need a password based key derivation function or PBKDF. A key derivation function based on a password is also called a password hash for short; it is also commonly used for password verification. Known PBKDF's are bcrypt, scrypt, PBKDF2 and the much newer Argon2 (in various forms). These all perform key stretching.