You got two options 
1) Make your base mesh in modo or ZBrush without uvs. Sculpt/polypaint it in ZBrush. Make sure your lowest subdiv level is at least a thousand polys (or more for certain situations), lower causes problems. Add uvs (lowest subdiv), I use puvs (4k if it’s really detailed). Hit tool>texture>new from polypaint (highest subdiv). Create either a displacement or a normal map (lowest subdiv).
If you don’t have GoZ, open the obj, disp/norm map, and texture map in modo. Enter subD mode in modo (tab) to view the sculpt. At this point, because it has uvs, you can continue to add or work on textures in modo, and even do it in layers like photoshop. modo is very much like photoshop in fact, which I like. It does have nice tools to further paint, sculpt, and texture your model.
2) Make your base mesh in modo. Make sure it has at least a thousand polys again. Create uvs in modo by selecting edges and uv unwrapping. Export to ZBrush. Sculpt, polypaint, create texture from polypaint, then disp/normal. Same as before. This is if you need uvs that aren’t automatically generated, such as puvs, and need to lay them out yourself. Good for certain things.
So yes, to get a true hi res sculpt from ZBrush into modo, you will need to use displacement or normal mapping to remain efficient.
Regarding polycount, modo is not the beast we all know as ZBrush! The ZBrush canvas can handle ridiculous amounts of polys. Meanwhile, modo can do some awesome modeling, scene set up, and renders. It doesn’t matter how much you beef up your machine, modo (at the time) will not be able to handle polys in the same manner. ZB and modo are two very different 3d spaces, both with great advantages.
However, in modo, you can sculpt on meshes or difference maps, such as displacement or normal. (mesh based vs. image based) This can be handy for a lot of models. I’ve seen some really good modo sculpts. This will save you from working in two apps, but you might find yourself missing ZBrush for most sculpting. Much smoother with more tools dedicated to getting the job done. Thankfully, they work really well together.
All that said, in my opinion, modo is flat out awesome. I recommend you spend the time to read through the documentation, which is done well, and work the tutorials. It’ll get you cookin’. 
