This is my question, I will make a board to control pyro ignition in rocketry using RP2350A. I plan to code this project via Arduino IDE, which libraries or additional files should I download, is it possible to code via IDE ? And do I need to install bootloader before coding?

You can. If your custom RP2350A board doesn't come with a UF2 bootloader pre-installed, you need to flash a bootloader.

OMG, don't do it before you really really know what you are doing !

All RP2040 and RP2350 have bootloader hardwired in ROM (from factory, non-negotiable).

Yes, the Earl Philhower core works amazingly well in the Arduino IDE. Well documented. Use the Board manager to install.

The bootloader is built in and works really well. If building a custom board, make sure to include run and boot mom-spst switches as shown in the hardware design doc from raspi.