Start with a "kitchen sink" style device that has everything you can imagine. Like a 40 or 28 pin device of the 18f4620 family, or the newer "K" series in similar size. For 16f devices the 16f887 family or newer 16f1xxx family. Verify compiler and programmer support for the newer chips.
When all the required resources (a-d, pwm, usart, comparators etc.) are determined, then a smaller PIC could be chosen with the assistance of the **broken link removed**.
One could also look to some of the Microchip demo boards for specific applications. They may already have what you want, like the **broken link removed**. The Mechatronics board is for a brushed dc motor, and as I understand it, some computer fans may be brushless? Board too expensive? then copy the freely availalble schematics to a protoboard, and learn from the demo software lessons/examples. All Microchip really wants to do, is sell chips.