I too was confused to bits. No, you don't need all the variations. For the vast majority of locos and rolling stock, you're best off with the 'standard' 1015 body-mounted coupler sets. You can get these assembled in pairs, or (much cheaper) in 10-packs unassembled, in your choice of black or brown. A Micro-Trains 'starter pack' which contains the gauges and assembly jig would be strongly recommended too. That's about all you need, really. I use:
MT starter pack (only need one of these, contains everything)
10-pack of 1015 couplers (10 pairs, that is), one pack per ten cars/locos you have
then, I also bought a 20-pack of MT trucks without couplers (for those that I need to change out), and a 100-pack of MT low profile wheelsets (for when I want to swap out non-low-profile wheels).
You only need to get involved with the complex stuff if/when you want to:
(1) convert odd locos, or very long passenger or autorack cars
(2) swap out trucks for the correct prototypical versions, if they're wrong
(3) errrr that's about it, I think
See, easy!
On the trucks you have, a sharp knife is all you need to chop off the existing couplers, and then you can install the body-mounted couplers...
Charles