Official comment
Hey Victory Road, I can certainly answer those for you, I'll give you the "here's how I do it" approach, and you can use this info to adapt to how you work.
When I load a track, I'll hit the PLAY/PAUSE button twice. This starts the track, then puts it into a "pause" mode, which I can then use to move the jog, adjust the play position to where I want it, then press the CUE button. That sets the main cue for the deck (which is only a temporary cue). If you want to set that position as a cue you can use again and again, either store it as a HOT CUE by pressing one of the pads (when the pads are in HOT CUE mode). You could also store it as a memory point, but you'd have to do that in the software or with a keyboard shortcut, as there is no direct button on the RR to do that. The nice thing about creating a hot cue at the start of each track for your preferred starting point is you can set a preference in rekordbox to automatically load the track to the first hot cue / memory point every time a song is loaded, so it performs those steps for you.
The second question is partially answered by virtue of having set a main cue point on the song -- if you want to go back to the start of the song and have it stop, press the CUE button on that deck. The deck returns to that temporary master cue point and stops playback. If you want it to return to that point and keep playing, press SHIFT+CUE. The other option here would be, if you've set a hot cue, you could press that hot cue pad to jump back to that position, and it will continue playback from there.
We have lots of videos on YouTube, definitely worth checking out.