Questions just write.

Shadow Dancer + Berserker boots give you the needed Walk speed that you would also have with boots of Swiftness, So it's not that necessary, also the slow helps you getting to your enemy faster.

I would buy a Frozen Mallet if you get ganked very hard and need the extra survivability + better slow, Black Cleaver is good as it gives you Armor Penetration + ATK Speed + More ATK. It is Situation Dependent on what your enemy team is.

Good build; but why wouldnt you get boots of Swiftness????
Also, have you tried using the Frozen Mallet, instead of BLack cleaver.