About Data spreading in CDMA
There's no lower and upper general limits, aside from the fact that you need to transmit at least 1 bit, and that your spreading sequence should be longer than 1.

By the way, you typically apply spreading to symbols, not bits. 

Spreading sequences can be binary, but they don't have to be.

So, bits is the wrong unit here; symbols for $i$ would be right, and chips for $y$.