Adafruit offers breakout boards based on the family of chips you are considering ([ADS1015](https://www.adafruit.com/product/1083), [ADS1115](https://www.adafruit.com/product/1085)). They even have some nice code examples for Raspberry Pi.

If you need extra analog inputs I'd suggest using an arduino board. Arduino Mega offers 16 analog inputs and you could communicate via USB, I2C, RS232 or SPI.