Greetings brother.
I have been growing perpetually, and exclusively with canna for the past 2 years. I also am in coco. I use 50/50 canna coco/perlite.
I would also like to raise a discussion here regarding optimal canna nutrient regimes and what supplements work well with the line. I may start a thread myself.
What i can add from personal experience is that, it seems regardless of the strain that it takes a heaaavy feeding to actually burn them. im fairly aggressive with my PPM and i tend to never see any harm.
Id like to add that i use the canna COCO line. you said that you are using vega? unless you know something i dont, id like to encourage you to switch to the coco line. coco medium is unique and a bit delicate in the way salts are dissolved and nutrient intake occurs. it is most favorable to use a nutrient line specifically for coco. and canna definitely was the way to go in that direction. they have the highest quality coco line for sure.
But anyways, in other words I would assume that it will be easier for you to overfeed, develop nutrient intake issues or salt build up using a more "hydroponic" or totally drain to waste line like vega. Bc i know the same is true for lines like Advanced Nutrients . burn them easy and lots of salt build up.
Another thing i can offer is that i have noticed that it DOES depend on the strain, but its about 50/50 chance that your plants will feel N or calcium deficiency using the ling as is, even in heavy feeding and especially during the first few weeks of veg. so i supplement ALWAYS just to be sure with a small dose of botanicare cal-mag at those times.
so as for your question on what to feed wk 1 ... heres wat i prime medium, and feed seedlings tiill day 7.
A+B = 3ml/gal
Cal-Mag = 2ml/gal
rhizo = 15ml/gal
Ph= 5.4-5.6
PPM=720-780
sound heavy?? idk. i never burn. different strain every month. always healthy dark green.
what strains do you have going there and how many times have you grown before? lets keep in contact maybe we can help each other out. when i start my thread i will send you a link to it and maybe we can get a good discussion going and maybe even a dedicated thread to canna nutes. good luck !