This is the very start of the project... I am just comitting the basic framework for now.
USE AT YOUR OWN RISK!
There are currently three supported hardware drivers:
Adafruit_PCD8544 (actually, any Adafruit_GFX display should work) for Nokia 5110 style displays. Currently only hardware SPI is supported - but this is just the constructor that needs to be copied...
Adafruit_BNO055 for BNO055 IMU
SFE_BMP180 for pressure (you can figure out your same way to connect a pipe to this sensor... some people place it in a small, sealed box... i took a 90 degree irrigation fitting, cut off one barb, heated the cut end until soft, then squished it over sensor (careful to avoid sense hole), held in place with cable tie, and fixed with epoxy)
There are plenty of howtos on the web for connecting each of these devices - I will not repeat them here - just provide some basic advice.
5110LCD - this is a 3.3V device. VCC must be 3.3V. The backlight can be connected to 5V through a resistor (I use 680 Ohm). The inputs are 5V tolerant, but it is best to connect them through a 1k resistor, just to be safe.
I2C devices. All the I2C devices are 3.3V. There are many different breakout boards, so you need to follow the instructions specific to the board you acquire. Most have built in 3.3V regulators, and can be connected to a 5V supply. Some have built in level shifters, and can safely be used with 5V Arduinos. Some do not have level shifters, but can be used on 5V Arduinos with some care. Since I2C is an open drain output, the HIGH voltage is set through pull up resistors. Every breakout board I have seen has built in pull-up resistors to 3.3V. So the I2C device will see 0-3.3V which is perfect. BUT the Arduino has a silly restricition on the I2C pins, that it requires 0.7*VCC (or 3.5V to guarantee that it will read HIGH). Ideally you should use a level shifter. But you can also reduce VCC to the arduino by passing the 5V input through a 1N4001 diode (or similar). When powered from the USB port, it already has a series diode, so works fine. If powering from an external 5V source, then add a diode so that VCC decreases to around 4.4V.