my current set-up is an atmega 328 (formerly on an arduino diecimilia) running on 5v on a breadboard (using tom igoe's tutorial). I use an FT232R breakout board to upload sketches to it. I now need to drop the set-up down to 3.3 volts for various reasons. My checklist of things to do (and my present answers) are as follows:
get clean 3.3volts: use a 3.7 lipo from sparkfun and the latest sparkfun 'power cell' which has a nice TPS61200 Buck/Boost Converter.
Doing 1, means that I can get rid of the 5v voltage regulator (and capacitors associted with it).
Change the 16MHz crystal to an 8MHz crystal.
Change the wiring of the FT232R breakout board so that it runs at 3.3v
Load the same sketch as before onto the chip from within the arduino software but this time select 'arduino pro at 3.3v at 8MHz'.
No, I think you have covered the points. However to save time you might just change the voltage and keep the 16mhz crystal. Several vendors sell 328 boards and can either be switched to 3.3v operation or are only available in 3.3volt version yet still run at 16mhz. While it is not in accordance with the AVR datasheet specs, most all report no problem running at 3.3vdc and 16mhz. Might be worth a quick check out.
If you change the 5V regulator for a 3.3V one you will still need 4.7uf to 10uf caps on the input and output of the regulator.
Otherwise it WILL oscillate.
The thing is i currently run the ATmega328P on the 3.3v circuit stirred over a Breadboard works well ,no voltage regulator no nothing just crystals and some supportive cap's and it does its game seamlessly.
you can run 3.3V w/ a 16mhz crystal but it can potentially cause problems with timing and baud rates. Its not that bad. I built 3.3v @8mhz boards for a low power gps project. If your doing serial or something timing specific then i would change crystals and bootloaders