I picked my battery up from a local battery supplier here on the coast. The also had a container to put it into (plastic but ok) where I could connect to external terminals or plug in a ciggie plug, plus it had a charge indicator on the top. very handy. Battery and suitable charger though aren't cheap. Few hundred $ all up from memory.
Yep jaycar will sell what you need.
Definitely if you are buying ethos stick to the visual for a while
or maybe try some planetary imaging where focal length is an advantage and a wedge isn't needed.