So you got the HP? What kind of lights are you using?
That Great White will work fine. I've never used it but others here have with good results. Worm castings work great with Pro Mix. I would use about 20%. Some like to use less but I always found 20 - 25% always worked good for me. Also, add as much perlite as you do worm castings. I also use other things like blood, bone and kelp meal. Pro Mix only has starter nutes so you've got to provide everything else either through amending, feeding or a combo of the two. pH it to around 6.2.
I use it for starting. I've found that by about 2 weeks I was seeing at little N deficiency, so I started adding a little blood meal. I also feed 1/4 strength nutes starting at around 2 weeks.