Magnet strength in dynamo design
When you talk about the "gauss strength of the magnet to be 8000-10000 gauss," there is some ambiguity as to what you might mean.  The strength of a permanent magnet can be measured in a number of different ways.  One of the most common ways is with a property called the Residual Flux Density, or \$B_r\$.  \$B_r\$ is independent of magnet shape - it is a characteristic of the magnet material.  

Typical \$B_r\$ values for different types of magnets:


Ferrite - 2000-5000 Gauss  
Samarium-Cobalt (SmCo) - 8000 - 12000 Gauss   
Bonded Neodymium-Iron-Boron (NdFeB) - 4000-12000 Gauss
Sintered NdFeB - 10000 - 15000 Gauss


If you can determine the type of magnet you have (probably one of the above 4 types) and then determine the grade of magnet, then you should be able to determine the \$B_r\$ for your material.  

The strength of a magnet might also refer to the field strength the magnet produces at a certain position with respect to the magnet.  This field strength is dependent on both the magnet material,the shape of the magnet, and how the magnet is magnetized (assuming the magnet isn't in a larger magnetic circuit).

You can't directly relate either of these measures of magnet strength to the amount of electricity it can generate because there are many other factors involved.  At the minimum, you would need to know the shape of the steel in your fixed, inner stator.  You would need to know the air gap between your magnets and your stator.  You would need to know how the stator coils are wound, including which teeth each coil goes into, how many turns, what size of wire, etc.  You would need to know the speed at which the magnet ring is turning.  

Those things are probably the bare minimum that you would need to know to determine what you are trying to determine.  As a comment above mentioned, there is software out there that can calculate what you are trying to determine.  Or if you took a course on electric machinery, you should have the tools needed to solve this problem.  It's a complex problem to solve and probably difficult to give you a full answer here on Stack Exchange.  I would highly recommend Fitzgerald &amp; Kingsley's book Electric Machinery if you want to delve deeper into this.  That book will give you a very solid understanding of what you would need to tackle this problem.