You could get by with only one of four bulbs if you'd like. Four bulbs seems like way too much. I would turn it down to just two bulbs and that would be a nice level that you can still grow anything and have nice coloration (1x 10k and 1x roseate, but ideally you'd swap the 10k for a 6700k, no big deal though).
Ferts will not add to your GH unless they contain Ca or Mg. GH booster ferts do contain these because they are designed to boost GH. Ferts like KNO3, KH2PO4, K2SO4, etc. don't raise GH, but ferts like MgSO4 (which is part of PPS Pro) and trace element ferts that contain Mg or Ca do.
As far as a regimen goes, I (and many others on this forum) like the Estimative Index method, or EI for short. This basically has you dose excess of all nutrients and then water change 50% of your water weekly to reset the system and not allow the nutrients to build up. I like this regimen because you can easily adjust it to you own needs and plants slowly over time to where you set a comfortable routine for yourself without ever worrying about deficiencies.
edit: WOW Hoppy just did a huge ninja on me. Covered everything I said in my post.
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