No, I don't fully understand the TLC5940... it's a black box to me, but I understand it can expand UNO's capability to 16 channels...
16 PWM channels with per channel current limiting. Correct.
Without using a TLC5940, I only have 2 maybe 3 channels from the UNO.
Or maybe six channels.
I had assumed the TLC5940 had it's own timer.
It does not. You are responsible for providing a clock signal on the GSCLK pin. You are also responsible for asserting BLANK at the correct time. The two commonly available TLC5940 libraries handle both of those tasks.
I don't know if the UNO must put out 25kHz to make the TLC5940 put out 25kHz.
Each clock tick advances a counter in the TLC5940. The counter stops (essentially freezes) at 4095.
So, if you use the TLC5940 library reconfigured for 25 kHz, the counter is incremented every 40 microseconds. The count goes from zero to 4095 (4096 steps) which comes out to about 164 milliseconds. That gives a cycle time of 164 milliseconds or a 6 Hz PWM cycle rate.
Which means you have to do two things: 1. Increase the clock rate. 25 kHz output from the Arduino equates to an essentially useless PWM cycle rate. 2. Decrease the number of steps. It is simply not possible to get 4096 steps with a PWM cycle rate of 25 kHz.
...then talk the TLC5940 into changing the duty cycle for the respective channel at 10% increments...
10 steps. For that you need to reconfigure the TLC5940 library for a 250 kHz clock output and reconfigure (or recode) the TLC5940 library to assert BLANK when the count reaches 9. Bear in mind that asserting BLANK has to be performed every 640 cycles of the AVR processor clock. That is a significant overhead which will not leave much processor time for the rest of your application.
I only require it be a digital 25kHz output (not analog).
That is a lie. You also stated...
...take some temperature inputs...
...which presumably also includes calculations.
If these components aren't correct to acheive my Goal, would you please suggest what is?
For outputting 16 PWM signals at 25 kHz with 10 steps an Uno + TLC5940 will most certainly work.
As for the rest of your goal, who knows. You haven't told us enough to offer an opinion.