Lens combo - for general use

[fess67]

I have 24-105mm and 70-200mm+1.4 extender. Is it necessary to get the 100-400mm or the prime 400mm for wildlife and birding?

I would say yes. The 1.4x + the 200 = 280 so still a fair bit shorter than the 100-400 will give you. Just be aware that the 1.4x will not auto focus with the 100-400 unless you have a 1x body.