I haven't found Moho to be terribly demanding on gear. To me, working in Moho, even on a modest laptop computer, seems really speedy. But that's probably because my background had mainly been in 3D and vfx compositing, where I could spend many hours, even days, setting up scenes and rendering. By comparison, most of my Moho scenes take a few seconds to several minutes to render entire scenes.
The hardware considerations should depend on your designs and whether you break out your scenes or insist on rendering everything 'in-camera'. You should also think about what other programs you may want to use that could more demanding than Moho.
For me, it's all about the RAM. Get more of it if you use a lot of bitmap art. Rendering high-re bitmaps (2k, 4k, and higher,) can gobble up your RAM and drag the system down to a crawl if you don't have enough RAM to support it.
If you plan to work entirely in vectors or use only limited, lower res bitmaps (i.e, texture fills), you can get away with a lot less RAM. For example,
HLF looks like it uses a lot of hi-res bitmaps but it was animated and rendered on a small 4GB laptop. This is because most of the art was actually vectors with lower-res, seamlessly tiling texture fills. If I had used actual hi-res bitmaps, I would not have been able to render this animation on the laptop.
However, there was an aspect to this project which did require a lot more RAM and CPU power. The 'Moho' part went very smoothly on the laptop because I used bitmaps in a limited way but also because I relied heavily on Layer Comps, which means I could easily break out a scene into simpler passes using the Layer Comps tools. A typical scene had one or two 'character' layer comps; 'FG', 'MG', 'BG', and 'Sky' layer comps for environment layers; and special matte passes if I felt I needed them. Even though this meant creating more renders, it also meant the individual tasks were much simpler for Moho, and it also meant rendering revisions were usually very fast to render (assuming camera choreography did not change.)
Where things got gnarly for me was everything
after Moho. I mostly broke out and composited the project in After Effects so I could add a lot of optical effects like DOF, motion blur and lighting tricks. All of this was very CPU intensive, and also RAM intensive because I rendered the entire project at 1080p as per the client's request. This really challenged my home workstation which only had 9GB of RAM at the time. I recall AE crashed in the middle of rendering often after I applied AE's Pixel Motion Blur. Fortunately, since I rendered to image sequence, I could just pick up the renders where I left off. Once I got my final composited renders, AE easily handled compiling the final movie files needed for editorial.
After that project, I upgraded my RAM to 18 GB and haven't run into this problem since.
At work, my computer has about 40GB of RAM, but I can push the limit there by keeping Moho, AE and Photoshop open at the same time.
So, short version: Get as much RAM as you can possibly afford. There are ways to work with less RAM but life can be much easier when you have more.