1. There are no limitations, you can do whatever you want.
2. Chat and video chat modules are not included, based on the user's feedback we plan to include a text chat and SIlverlight-based video chat in Q4/2011 or Q1/2012. Events module is included in the default installation.
3. Yes, you can develop unlimited number of sites with it.
4. I would not say that there are many error reports - most od the support question are related to the installation and configuration issues, or are custom development quieries. In any case, priority support is included with the source code purchase: 24 hours max response time, private discussion board, access to the latest versions, direct contact with the development team.
5. There are no discounts at this time, and the price is $2999. We were considering some changes in the licensing scheme (source without support, single site licenses), but none of them proved successful. MonoX is probably the least expensive solution in its category when you take into consideration all the factors, including the level of support and the existence of hidden limitations on the number of sites or modules that the license covers. Many of the competing commercial and open source products start free or for a low price, but than there are problems with the performance or support, licenses has to be purchased for each subsequent site you build, all modules are not included in the base price, etc.