If I have a PCB with an bootloader-installed Atmel chip (e.g. ATMega328p), and I want to have an easy way to upload sketches to it, would I use an ICSP header on the board connected to the appropriate pins on the chip?
Like, can I use something like this? https://www.sparkfun.com/products/9825 ....and upload sketches from the Arduino IDE? Or is the ICSP connection on the chip only used for bootloader programming?
Maybe an FTDI connector on my PCB? Would that work? I'm assuming I just need to do serial programming from the Arduino IDE...
If you have the bootloader installed you just need something to convert USB to TTL-serial. An FTDI converter can do that. Your standalone circuit must allow the FTDI converter to cause the Atmega 328 to reset when required by the upload process.
You could also do it with an Uno if you carefully remove the Atmega 328 and connect your standalone 328 to the Tx and Rx pins (Tx to Tx etc) - and GND and RESET.
An FTDI cable (USB-TTL cable) is a very convenient thing to have as you can use it with different standalone projects.