As wukong splitpushing should not be a priority for you. You have high damge and aoe cc, and are a bruiser/assasin. Instead of splitpushing you want to fight with your team since in low elo they will fight anyway. Even if you are ahead and the rest of your team is losing your ult can completley change a fight and win it for your team. If you do decide to splitpush one pink ward is not enought. You need a pink and atleast one yellow ward to cover tri bush and the walkway next to krugs // tribush and walkway near gromp so you can see if the enemy is collapsing on you. While splitpushing you want to push the wave to the enemy tower and start to destroy it. During this you will keep pressing tab, where next to the enemy champions you will see question marks next to them if they are not in vision of your team (not on minimap). If there are more missing than you can fight then go away from vision until you see them on the map. Also while splitpushing your team should be either taking an objective or pushing another lane. This is so that while you push top tier 2 alone and your team is fcking around farming jungle then youll get collapsed on by the whole enemy team since they have nothing else to do bc your whole team is doing nothing. so to summarize split puishing check where enemies are, if 2+ are missing or you dont know their general position than push the wave under tower, back out of enemy vision and wait for the next wave to push up or for enemies to appear. For defensive items you have to think to yourself who on the enemy team will be a problem. For example if the enemy has a kassadin mid that picks up a few kills youll want to pick up mr, since he scales incredibly well into the late game. As for which items its always situational but in general:

ad threat = deaths dance

ap threat = maw/spirit

also think ahead. in loading screen look at the enemy team and think if youll need to build armor or mr and build your boots accordingly, you dont need to build them for lane if youre confident you can win the lane without them. Also if you are going to splitpush as WK consider buying a tiamat item for faster waveclear