Canna nutes work just fine, I think CannaBoost is a bit too expensive though, I picked up a free sample at a show and I didn't find it made much difference,(it is supposed to increase the plants rate of photosynthesis) I have one more bottle spare so I am planning to try it again in the future.

I mix my nutes about an hour or 2 before I use them. I seem to recall that this is what it says on the bottle. I have no idea what difference it makes.

The best feeding charts for Canna nutes that I have found are in my photo album, check them out. The official Canna feeding charts are a bit crap in my opinion, they are not that easy to follow for novice growers. I have used the full range of nutes and also just basic veg+flower nutes and PK. When I use the full range my plants do marginally better, but I think this margin will increase now I have better lighting.

I have also tried Dutch Pro and VitaLink, I have not noticed any noticeable difference in growth over the 3 brands, they have all worked just fine and havn't needed much tweaking to the feeding schedule to get decent results. I am currently using Canna Hydro Vega+Dutch Pro Take Root for veg and Dutch Pro Original Bloom+Dutch Pro Boost for flower, with an occasional dose of cal/mag and sea minerals.