New Project: Temperature Measuring with MLX90615 [please help, this is my first project]

Hi,

I started a new project, which I want to get pcbs made for. This is my first ever own designed circuit and I don't want it to fail or cost me more money because of some stupid errors.

See the schematics for the whole thing i created.

I have some questions, which I'm not 100% sure I did the correct thing, please feel free to comment and add ideas, I'm new to this...

Why did I use a demux? Because I want to display the unit Celsius or Kelvin.

1. The transitors (MMBT3904) are for disabeling the power supply for the demux and the 7 segment displays. Because this will be powered form a single CR2032 coin cell. The Sensor has a sleep mode so need for the sensor. Can I use this Transitors? I want to order transistors which I can use in later projects...

2. Are the values for the resistors correct especialy the base resistors? I did calculate them, see added picture.

3. Do I need a quarz for the msp430 to interface correctly with the MLX90415 temperature sensor?

4. Is the MLX90615 correctly wired? I want to use SMBus

5.PIN3 of the MSP430 is for measuring the voltage of the battery, I want the msp to power off everything when the voltage is below 2.6V.

4. The switch is for waking the msp430 up and/or starting a measurement. Later switching between the Units.

6. I want to use 0805 resistor type, do you think there is a problem?

I appreciate any Idea, correction, Everything! Thank you very much...