I've only used Maya for a very short time years ago, so I cannot say anything that relates to exact procedures, but one thing you can do is get
Netfabb Basic, which is free, and use it to scale your creations using the scaling functions. The software is specifically designed to help facilitate 3D printing, so the output is designed for the real world.
As for making sure that what you design in Maya is in conjunction with real life measurements, do some tests and create a pipeline where when you export a one inch cube and have it 3D printed it will come out of the 3D printer as a one inch cube. Also, if you're going to be making toy figurine accessories, which you can sell on Shapeways by the way, be sure to get a digital caliper. Since you're not building space shuttle parts you don't need an expensive one, just a cheapo
like this one will do just fine. Best $12 you'll ever spend!
This will let you make super accurate measurements that you can then use as the foundation stones of your creations.
Yes, Zbrush can be used. Everything I've created over the years for 3D printing has had Zbrush involved. The million triangle limit can be annoying at times, but most of the time one can get by with this limitation in place.