user-1: I have a custom PCB with a 32u4 running fine with an 8MHz external oscillator.  I burned the bootloader and loaded my sketch with an UNO using Arduino as ISP.  
I have no USB on my PCB nor do I need precise timing, so I wanted to see if I could simplify things by removing the external oscillator and caps.
Reading the 32u4 datasheet it states "The device is shipped with Low Power Crystal Oscillator (8.0 - 16MHz) enabled and with the fuse CKDIV8 programmed".
With that, can I simply hook my PCB (assuming a factory fresh 32u4) via ISP to the UNO as before and in IDE just use Sketch > Upload Using Programmer?    Basically not burning any bootloader at all.  
Also, in IDE I have been choosing the Sparkfun ProMicro 3.3v, 8MHz board.  Can I still use that selection?

user51836: Yes you can reprogram your 32U4 chips via the ISP, they do not have to be fresh chip. If you set your Fuses to -U lfuse:w:0xE2:m -U hfuse:w:0xD8:m -U efuse:w:0xCB:m using AVRDUDE you will have an 8mhz internal RC oscillator set and you do not have to have the external crystal.
You can play with these settings at http://www.engbedded.com/fusecalc/.
I recommend learning the command line AVRDUDE commands this way you have more control over what you are doing to your chip.
I use this all the time, and if you need to do more than one quickly I typically make a batch file that does the Fuse Burn and hex at the same time.
this is for a attiny167 but you get the idea:
.\avrdude\avrdude -C".\avrdude\avrdude.conf" -v -pattiny167 -cstk500v2 -PCOM3 -Ulfuse:w:0xE2:m -Uhfuse:w:0xDF:m -Uefuse:w:0xFF:m  -Uflash:w:1060X01-001.hex:i

-1: <p>I have a custom PCB with a 32u4 running fine with an 8MHz external oscillator.  I burned the bootloader and loaded my sketch with an UNO using Arduino as ISP.  </p>

<p>I have no USB on my PCB nor do I need precise timing, so I wanted to see if I could simplify things by removing the external oscillator and caps.</p>

<p>Reading the 32u4 datasheet it states "The device is shipped with Low Power Crystal Oscillator (8.0 - 16MHz) enabled and with the fuse CKDIV8 programmed".</p>

<p>With that, can I simply hook my PCB (assuming a factory fresh 32u4) via ISP to the UNO as before and in IDE just use Sketch > Upload Using Programmer?    Basically not burning any bootloader at all.  </p>

<p>Also, in IDE I have been choosing the Sparkfun ProMicro 3.3v, 8MHz board.  Can I still use that selection?</p>
 51836: <p>Yes you can reprogram your 32U4 chips via the ISP, they do not have to be fresh chip. If you set your Fuses to <code>-U lfuse:w:0xE2:m -U hfuse:w:0xD8:m -U efuse:w:0xCB:m</code> using AVRDUDE you will have an 8mhz internal RC oscillator set and you do not have to have the external crystal.</p>

<p>You can play with these settings at <a href="http://www.engbedded.com/fusecalc/" rel="nofollow noreferrer">http://www.engbedded.com/fusecalc/</a>.</p>

<p>I recommend learning the command line AVRDUDE commands this way you have more control over what you are doing to your chip.</p>

<p>I use this all the time, and if you need to do more than one quickly I typically make a batch file that does the Fuse Burn and hex at the same time.</p>

<p>this is for a attiny167 but you get the idea:
<code>.\avrdude\avrdude -C".\avrdude\avrdude.conf" -v -pattiny167 -cstk500v2 -PCOM3 -Ulfuse:w:0xE2:m -Uhfuse:w:0xDF:m -Uefuse:w:0xFF:m  -Uflash:w:1060X01-001.hex:i</code></p>
