Good hydro shops will sell the "Canna Terra Professional" range of soil which is specifically designed for our favourite plant, and includes perlite and worm castings. I am not sure on the specific potting mix you posted - I don't have any experience with that one. One option if you don't buy the Canna stuff could be to get a bag couple of bags of potting mix, a bag of composted chicken manure and some perlite, blood and bone etc and make your own. I went with the Canna soil because it is made by a reputable company and is a "known quantity" so to speak. And I raised my seeds in it and have been using the Canna Terra Vega and Canna Terra Flores nutrients just to keep things simple this time around. For my next grow though I might just amend the soil with rich organic nutrients like blood and bone etc that I previously mentioned, something like the TGA Subcool "Super Soil" with all the good nutrients in it that plant can use throughout the entire process.
Specifically in relation to raising seeds, I don't think you can go too wrong with a good quality seed raising mix, the nutrients in there are likely to be at low levels, low enough not to burn the plant. And weed is very resilient. Don't make the mistake I and most noobs have done which is to overwater. Jiffy pellets are okay and I have used them but be aware they do hold a lot of water so you will not need to water them very often to begin with, if you use those.
The Mandala Seeds website has some
excellent information on all aspects of growing, I highly suggest spending some time to read through it - you may not buy this brand of seeds but it is relevant to all brands of seeds, obviously:
http://www.mandalaseeds.com/Guides/Germination-Guide
Look for more info in the "Grow Guides" link at the top of the page.
About ordering seeds, I've ordered twice from Herbies Head Shop and post times have had no dramas - and they are very helpful.