As far as uploading shapefiles, the size is limited by what the browser can display. Generally, less than 750 features. This is, however, impacted by the number of vertices your lines/polygons contain. You can consider generalizing your data before uploading it.
The planned time frame for release is in conjunction with ArcGIS 10.1, so first quarter 2012. That is our target. Unfortunately, pricing has not been finalized. I'd suggest contact your distributor for more information.
Thanks,
Mike