You can use this calculator, http://calc.petalphile.com/
. The fertilizers are listed as molecular formulas ie. Potassium Nitrate is listed as KNO3 and Potassium Phosphate as KH2PO4. The magnesium you have is most likely MgSO4.7H20. I watched the video and it did not appear to be anhydrous magnesium which looks more like a powder. What he used appeared to be granular like MgSO4.7H2O, btw that's epsom salt.
The doses recommended looks pretty good. When you use the calculator select the solution radio button and it will display a container size and dosing size for mixing. As far as magnesium, remember you may have some in your water supply. It may not be necessary to dose at full strength.
Not dosing the potassium nitrate may leave you potassium deficient. Typically with EI dosing, the potassium comes from the KNO3 and KH2PO4. When you use the calculator look on the right side. It breaks down each fertilizer dosed into individual nutrients.
Having a nitrate of 40ppm regardless of water changes tells me your test kit is not accurate. If you have a nitrate of 40ppm before a water change it should go down after the change. Check out this thread, http://www.plantedtank.net/forums/showthread.php?t=83545
for calibrating your test kit. This will tell you if it is your test kit or not. Besides it's a good idea to calibrate them anyway.
Once you determine why you have nitrates so high and eliminate it you can start dosing the KNO3 which will supply the necessary potassium.
As far as the micro mix I have no idea what they are using. From the suggestions they made for the others I would presume the dosage for the micros is accurate.