The only detailed accounts we have about Alexander from ancient writers are Plutarch, Arrian and Curtius who all write hundreds of years after Alexander’s death. Plutarch’s Age of Alexander and Arrian’s Campaigns of Alexander are the books you will want to pick up if you want to read about Alexander in detail. They got their information from contemporaries of Alexander such as Ptolemy, Callisthenes and Aristobulus (their accounts have not survived). I studied Alexander at A-Level and our spec did not include Curtius as essential reading so I haven’t read a lot of it myself but I do intend to at some point. In any case if you want to read Curtius it is The History of Alexander. All three books have excellent penguin classics translations.

Plutarch focuses a lot on the character side of Alexander’s life (religion, motivation, upbringing etc.) which makes for very entertaining reading.

Arrian on the other hand focuses on the nitty gritty, things such as administration, generalship and leadership. Not difficult to read at all, but not as entertaining as Plutarch.

Like I said I haven’t read much of Curtius but I believe he is more akin to Plutarch than Arrian.

One last thing is that Plutarch and Arrian want to portray Alexander in a good light and so justify many of his actions even if they shouldn’t be. Curtius on the other hand is much more critical of Alexander.

For the Wars of the Diadochi specifically I am afraid I can’t help you too much. Some of Plutarch’s lives in the Age of Alexander after Alexander’s death cover some parts of the Wars of the Diadochi, but I can’t give you anymore than that.