PCB Design - Simple USB Radio Transceiver
My advice: start with reference demo board, MCP2210 Breakout Module. Follow their BOM and layout to the letter, including RESET area, since your "design consideration" questions would require several pages of explanations.

Then add the radio module, again in full accord with manufacturer's application advises and demo boards. This should take care of use of GND pins etc.

Then apply the main architectural idea for an embedded design: (1) power-on HOST (master) first (in your case it is SPI bridge); (2) hold all slave peripherals inactive until the SPI host is activated (from USB side). (3) Use GPIO to enable the slave(s), which might include power gating and definitely RESETs of proper polariy; (4) activate the slave(s) across the USB-SPI-bridge as software/firmware is ready.

This approach should take care of all slave RESETs, and avoid excessive inrush, etc. Push-buttons should be placed only on development boards.