The amount of substrate will depend on the depth you want, I had to do some conversions to figure out some of your answers in non-metric. You need to measure the length x width x depth to calculate amount of substrate.
For 1 inch of substrate= 33 pounds or 15kg
For 1.5 inches of substrate= 50 pounds or 23kg
For 2 inches of substrate= 60 pounds or 27kg
I usually use about 1 inch of substrate in my tanks but they aren't truly planted. If you will be planting with plants that have or will get large root mats, more depth can be used.
Jeeco Aquarium Vacuum Gravel Cleaner is nice, instead of manually starting the suction. I use this and a 5gallon bucket weekly to clean gravel/do water changes on my 55gal tank. I use the pump button and hold in rt to get the siphon started, suck up some gravel a few inches up tube, then fold or kink the hose with lft hand to stop suction and release the gravel back. Then unkink to let all the lighter nastiness float up and get sucked out.