You were working on correcting the lighting, which needs a bit of tweaking. The powersun MVB is UVB and basking light/heat in one, and should be placed directly over the basking spot (no screen), at the minimum distance recommended by the manufacturer, and can be raised to acheive the correct temperature, if the temperature doesn't get high enough you can use an additional light to for extra heat, or a CHE (ceramic heat emitter). It's easier to mantain the correct basking temperature if the basking spot is solid and absorbs the heat, I'm unsure about the use of a hammock for basking, since I've not used one. Basking and UVB exposure go hand in hand.
The hides ensure that the dragon can get out of the heat and/or UVB when he needs to. Beardies regulate their UVB exposure in nature according to their bodies need to create pro-vitamin D3, and they'll do the same in captivity if the habitat allows it. The other basking bulb (or a regular clear light bulb) can be placed wherever extra heat is needed, to maintain an ideal temperature gradient and to provide additional light. If the additional light makes the enclosure too warm, then a regular linear fluorescent light can be used to provide additional light with very little heat, beardies require a bright environment to thrive. The thermometers are fine (I use as probe on the basking spot and one of those dials on my cool end to measure the air temp, I place the digital probe beside it weekly to make sure it's accurate).
You need a hygrometer, to measure humidity, especially if you live in a humid environment. Particle subtrates pose various health risks, depending on the material, and many (all?) will hold moisture; warm, moist substrate is a breeding ground for mold and bacteria. I would avoid them completely if humidity was an issue. If you had found the humidity too high, then you can use a dehumidifier in the room where the enclosure is kept. Maybe they make ones specifically for terrariums?
The vitamins and calcium should be used on a schedule based on age, for juveniles it's calcium w/D3 dusted 1 feeding per day, 5 days/wk. Vitamins are dusted 1 feeding per day, 2 days/wk. I dust calcium Mon-Fri and add the vitamin Thurs and Fri, leaving the weekends out, which is better for my forgetful self
I believe that when using an MVB the calcium should be without D3.
I'm sure others will add to this, if I've made any mistakes or left things out
Don't kick yourself for his passing. We all do the best we can with with what we know and have! You loved him and did your best.
You're learning all you can to prevent possible problems in the future, should you own another beardie, and to teach others. That's a wonderful thing for you to do!!
Take care of yourself, and again I'm so sorry, losing a loved one is never easy
Amy