I asked this some time back, a previous time Africa was a theme, and never got an answer so figured I've resurrect it.
In any case, I certainly know little about Zulu warfare in the first place, and what I do is basically '19th century. My understanding is that their style of warfare underwent a veritable revolution under Shaka Zulu in the early 1800s, changing how the military was organized and implementing the famed 'Bull Horns'. I know that there is some debate on how much it can be said this was influenced by the contact with Europeans, and the extent to which that is true certainly interests me, but I'm also especially interested in what the 'before' was.
To answer your first question:
Guns were present in Natal from the time Shaka Zulu created the Zulu Empire - Shaka even hired/conscripted very small numbers of Europeans with muskets to fight for him, although never in decisive or significant numbers.
The primary Zulu weapons from the time of Shaka Zulu until the Anglo-Zulu War in 1879 were a throwing spear, the short assegai stabbing spear, and the heavy knobkerry club. The spears would be thrown when the Zulu charge was about 20-30 yards away from the enemy - then the warriors would drive the charge home to use their assegai and clubs.
The European transition away from flintlock and caplock firearms around 1850-1870 lead to a glut of surplus muskets flooding the world market. A large number of these ended up in Southern Africa by way of traders in Natal and Mozambique. The most common firearm in Zululand by 1879 was the trusty old Brown Bess flintlock musket - by thenb it was so cheap, it could be bought by a Zulu warrior for about the price of a sheep.
The Zulus did some skirmishing - the "chest" of the bull formation would sometimes be preceded by shooters who'd throw down generally inaccurate harassing fire. Other warriors with guns used theirs as a kind of replacement for the throwing spear - they'd fire their guns at short range and then charge in to use their assegai.
I've written more about the subject of guns and Zulu tactics here: