Seems like a poor choice of chip.
Low on IO, only 9 pins - need 4 for SPI, 2 for water sensor serial, 2 for bluetooth serial, only leaves 1 for anything else.
Low on serial ports, sorta has 1:
"The Universal Serial Interface (USI), provides the basic hardware resources needed for serial
communication. Combined with a minimum of control software, the USI allows significantly
higher transfer rates and uses less code space than solutions based on software only. Interrupts
are included to minimize the processor load."
Low on SRAM and flash memory, 512 bytes and 8 kbytes.
You could try it, and when you run out of memory, move to a bigger chip to continue your programming.
The