From looking at the pictures of your telescope it looks like the focuser accepts the 1.25" eyepieces directly. Is this correct? or does it have a screw off part that exposes threads? In either case, I think this 1.25 inch to Eos adaptor might work for you. Not sure how to know if you would need spacers without trial and error, but your reason for needing them sometimes is spot on.
T-ring is just an adapter that fits your specific camera make's lens mount (so EF for Canon, F for Nikon, A or E for Sony, etc.) You usually get them with an adapter that slides into your scope's eyepiece socket (1 1/4", 2", whatever.)
This, for example.
I don't own a star tracker because I'd intended to shoot through the telescope first; my SC is a goto scope and the Newt has a battery tracking motor on it, so not needed. Also, I need to figure out S. polar alignment before I go blowing any more cash on gear :D
I may at some point, but want to screw around with my scopes first before investing in something like that; if I do decide to seriously go photographing, I'll probably drop on a Hyperstar first, though.
If you have access to a telescope and just want to mess around, try something like this first. Compatible with the majority of "standard" eyepiece telescopes.
https://www.amazon.com/dp/B00T4IRJPI
There are much better adapters out there, but all basically do the same thing. Some specialized eye pieces from Celestron have better adapters with better seals.
In addition to EF telephotos, you can also use something like this to fit your SL1 directly onto a telescope.