I'm not knocking the dry fert idea.... so don't take this the wrong way. It sounds like it will work fine and provide a better level of customization if you know what needs to be changed.
I think I bought a 250ml bottle of flourish comp for about $7 and, based on usage so far, it will last me the year... say even 6 months if I started double dosing in my 37 gallon tank. It's dead simple, covers the bases, not expensive... cost is slightly more than a single bunch of plants... and doesn't go bad. A bag of tabs will last about the same and cost about the same. So $14 for a year's worth of fertilization, hard to use cost as a factor.
I would wonder what the real justification is to switch from that to measuring little tiny portions of the various nutrients, various containers, mixing solutions (dry dump gets around that I suppose), sourcing everything.
I like a little complication as much as the next anal retentive detail freak... but some things, if not really necessary, are hard to justify. Particularly when simple works just fine.
Jeff.