What is the maximum number of pins that can be connected to stuff (like led’s motor controllers etc) on a Usbzi Fez?
The number of the io pins on the microcontroller is one way to count.
You also have to remember the specs for the power output capability of the chip - there’s an overall supply max through the chip as well as a per-pin max. So driving other logic would be fine but driving many LEDs might be more trouble
So basically connecting to much stuff to a Fez Rhino is a bad idea? How do I use all the pins without having to worry?
What are you trying to do?
Basically, drawing too much current above the pin and chip spec is a bad idea; you’ll have to explain more about what you’re trying to achieve before generalisation can be applied 
I have a Fez Rhino with the Wiznet module on it. That module uses alot of pins. Are there pins on the Breakout that I should not use if I’m using the Wiznet Expansion?
Did you check the schematics?
I was trying to but the whole thing was so confusing.
(I haven’t been well so sorry for the slow response).
I am trying to work out why the Mini CNC’s spindle speed controller seems to stop responding when I press a keyboard button. I eventually just got tired of trying to figure it out. I took all the electronics apart and now I’m soldering wires where jumper wires once existed.
Should I be connecting stuff to Fezes via 10K ohm resistors and transistors as a general rule of thumb?
If you need more current than the pin can supply, yes. If you need more total current than the MCU can supply, yes. Otherwise, maybe.
depends on what kind of “stuff” 
Well, currently I’m using 28 of the Rhino’s pins to connect a QuadStepper, but its inputs are CMOS. I need to connect a Speaker, a Motor controller and some push buttons to the mix as well. I have some level convertors that I purchased in the hopes that they could help but so far nothing good [url]https://www.sparkfun.com/products/8745[/url]
Well, if you’re only signalling between the devices and the Fez, you should not run into current issues. If you were powering a downstream device off a Fez IO line (so you could turn it off for example) then you might get into the kind of region you’re worried about, but I don’t think you’re likely to be there yet.
Depending on a device you connect to you can also use pull-up to +5V and output low to turn on the device.
I think the problem is with the PWM pins. I think that when I set one of them the others turn off, or are otherwise interrupted.