In the sub-tool palette there's a "Project All" button, which projects one sub-tool onto all (or maybe just all visible) other subtools. Select your low-poly retopology and click "Project All" (you probably don't need to, since you would've built it on-top of the other model). Then subdivide, and use Project All on the higher subdivision. Keep going until you have all the detail you need.

ZBrush doesn't bake normals by tracing from a low-poly model to a high one. It does it by getting the normals of the highest-subdivision mesh and projecting them onto whichever subdivision you have selected when you generate the normal map. It's not what I was used to, for sure, but with the freedom to sculpt extra details into the high-poly version of the retopo as you see fit, it's easier IMO to make a flawless projection.

For making UVs, if you have UV Master the video explains it in detail. But the basics are: select your model, open UV Master, click "Work on Clone" (or something like that), "Unwrap", "Copy UVs", then go back to your original low-poly model and click "Paste UVs".

Jibb