"In between" is often seen as incorrect by grammar snobs. It makes sense for Duo to steer you you towards "correct" speech, just in case someone cares. Additionally, I've lived in the Midwest, Northwest, and South in the US and I've never heard "cycle". Are the "cycle"ist commentors from a specific region?
It varies. Coche, carro, auto... They can all mean the same thing, but a speaker well definitely have a preference (and sometimes a strong opinion regarding the use of the other words). Different regions tend to prefer one over the other. I've heard all three of them. For some reason, descendents in the USA of Mexican immigrants seem to prefer 'carro' while all over Mexico I almost always hear 'coche' with an occasional 'auto'. Perhaps it's the similarity to 'car'.
SER ES PARA LAS COSAS QUE SE QUEDAN SIEMPRE DE LA MISMA MANERA. ESTAR ES PARA LAS COSAS PASAJERAS. If you say ESTOY ENFERMO ( i am sick) it means I am sick in this moment, not always. BUT if you say SOY ENFERMO it means you are sick all the time, from your birth even, it is your inherent nature to be sick.
"cycle" sounds like a very colloquial term. I've only every heard "bike" which is what I use for the more accurate "bicycle" and which, situationally, may actually mean "motorcycle". Growing up in Dallas, Texas and through popular media, I call those who ride bicycles for fun or sport as "cyclists" and motorcyclists as "bikers".
Estar is generally used for locations. (Although there can be exceptions, such as the location of an event such as a party.)
It may seem strange to us, but estar and ser are completely different words to native Spanish speakers, just as "do" and "make" are to us. The difficulty for learners is when it's the same word in our language, so we need to think about it and make a choice. For native speakers, it's just natural and there is no choice.