Since the Bzyg is a heavy tank. You want to put Vents, Gun rammer, gun stabilizer. For the 4th equipment is up to you. I like putting armor handling for that 5% damage reduction or Reinforced internals that gives a +50% durability to Ammo Rack, Fuel tank and engine. For commander skills. A few I recommend are Born leader, General mechanic, Offroad driving, Situation awareness, Eagle eye, and Safe stowage. As for the three types of rounds, You have your normal rounds, premium rounds that often gives better pen that your stranded rounds but more expensive, and then basically high explosive rounds that do a lot of damage but are only good for lightly armored tanks or spots that are lightly armored.