Thanks for the reply. On the board I'm about to design all the decoupling capacitors will be placed accordingly, the crystal (and its two 22pF caps) is just 4mm away from the OSC1 and OSC2 pins.
I'd like to avoid placing a USB header on my board because I just want to be able upload the bootloader and the sketch one time only. The ideal would be to be able to use an Arduino UNO board to help with the bootloader and program upload. Hence I need to know which pins need to be accessible.