Rob
Ansys Employee

If you drop energy URF from default (usually 1.0 but 0.75 for PBCS) you may find you need a LOT more iterations to reach the solution. It's OK to decrease the URF to get a model going, but you need to get back to the default by the end of the run. 

Re radiation & combustion models. These depend on what you're modelling. DO will cover most of the P1 capabilities, but P1 is no where near as comprehensive as DO. You may find S2S or Monte Carlo are better suited to your needs: again you MUST understand their use and limitations. The User's Guide and Theory Manual are fairly good in this respect. 

Area averaged values are good to get an idea on convergence, but will also mask moving jets and the like: ie the mean is always more-or-less the same but the jet wanders around. Use points and save images every some iterations to see what's going on. 

Have a look through the tutorials and videos in the Fluent Help system.