My first immersion chiller was just a 25’ copper flex coil bent into an approximate shape, with some high temp tubing hose clamped on and a faucet adapter for the sink. Worked fine. Be careful with a snowbank, you actually want it in a water bath in the cold. Snow is a great insulator, so as soon as the layer immediately touching the pot melts, the small air space around the pot will slow down the heat transfer.
Also, the wort in extract is already boiled, so as soon as it’s dissolved it can pretty much be fermented. No boiling is necessary if everything starts out sanitary. The boil in your kit is just for hop extraction.