IWS looks like a nice system and easy to get going with!
So yes, your flood time will vary depending on how long it takes the pump to fill the area you’re flooding. There’s not really any advantage in keeping the flood going any longer than you have to. Just enough to fill up your pots. Flood just long enough to saturate the root zone, and add a bit extra time to be safe.
For my setup, I timed how long the pump took to fill the table to the automatic overflow valve, and it happened to be about 6 minutes. So I added 2mins for safety.
Yes definitely with nutrients each time. The beauty of this system is that you just have to maintain the reservoir itself. A simple daily pH and EC check (takes about 5-10 minutes tops) and adding in some pH+/- to balance things off is really all it needs once it’s dialed in.
Then a top-up of nutes every 1 week, and a full res change every 2-3 weeks (ideally 2 weeks, but I’ve let it slip longer).
Young, small plants will probably only need about 2 floods a day, but you will probably want to move up to 4/day or something like that once they are getting big and hungry and you notice the pH climbing and the EC dropping really quickly in the res each day (this means they are consuming a lot more).
Canna will do you just fine I’m sure!! And yeah most def, keep that coco out of there and your plants will love you for it! The extra oxygen around their roots is the best thing for explosive growth