DWC 5 Gal Bucket, How to and when to?

I'm switching from Soil-less to DWC.

Already bought a 5 Gal Bucket W/ Bottom Drain + Net + Air Stone & Air Pump

I didn't have enough space to get a full pump system so I need advice on how to grow this way since it will be my first time.

So growing in Hydro, how often do you completely change the water, and how do you change it without a backup res*?

Make sure you read the stickys. But usually you completely change the soup once a week and top up every day or two.

At least once a month drain and refill. It won't hurt to drain and refill because the bucket should be in an aeroponic mode with 100% humidity in the bucket.
I always have my replacement water all set ph adjusted and right after I'm done draining I close the valve and with a spare water pump I just pump the new water right in. I used to leave a pump in he bucket but that didn't always get all of the water out.

Sounds like a good plan, hopefully Hydro isn't too complicated if anything I can always go back to coco till I fiddle with Hydro enough to feel confident to grow in it. All those roots I'm scared I'll damage the plant late in flowering and waste a few months time.

get a pH meter and a TDS meter - you will need it

I've been down this path, tried a lot of different things. Flushing, whatever...I found if you use distilled water, you never have to change. Plants in a 5 gallon dwc at 4 weeks will drink about a 1/4 gallon EVERY day. do the math. Using the right water, you never have to flush