As for your first step - with a project that size (and thus of substantial age, I assume), there's surely tons and tons of dead code. I'd throw it away first. S

As for your first step - with a project that size (and thus of substantial age, I assume), there's surely tons and tons of dead code. I'd throw it away first. Slim the thing down. The very process of identifying unused code will already familiarize you roughly with the conceptual "shape" of the application