What's with all this 1960's way of drawing circuits
It's called "ASCII art". You will see it in many posts on this site and others. It began in the 1980s as a simple and quick way to draw diagrams that were so simple that a proper graphical drawing wasn't worthwhile. It's also easy to quote. It's less common now because text is normally displayed in proportional fonts, so things don't line up reliably unless you force a monospaced font, and graphical drawing tools and image manipulation are a lot easier nowadays. But it still has its place for answering simple questions.
t = R C. The optimum time constant depends on the PWM frequency, the tracking speed (time to settle after a change), and the amount of ripple that can be tolerated. There is naturally a compromise between the last two characteristics - heavier filtering means less ripple, but slower response to changes. Performance in this respect can be improved by using distributed PWM (DPWM) with a shorter time constant, but the PIC doesn't support DPWM. It can be implemented fairly easily in an FPGA though.
BTW regarding your design in post #46. I think I see what you're trying to achieve. It's an interesting idea and could give significantly improved performance over the simple R-C smoother if you used a sample-and-hold circuit, but I've never seen that technique used in practice. Probably because of the cost, size, variability with temperature, and the need for calibration. An engineer would just spend a few more cents on a microcontroller with a built-in DAC. And that could be good advice for the OP on this thread too. But it's an interesting idea nonetheless.