Tankbot - An Arduino-based fish management system

Hello all,

This is my first Arduino project, and I'm wondering what kind of challenges I might face building this project. An overview of the project:

I want to build an Arduino project that will sense the amount of light entering my fish tank, the temperature of the water in the tank, and know the time.
It will use this information to operate the heater and a light in the hood of the tank to achieve a user-determined temperature and amount of light per day. It will also use a micro-servo operating a 3D-printed hopper to dispense food to the fish at given times in the day.
My user interface would be done through a serial port connection to my desktop computer.

Problems I foresee with this include:
-Waterproofing the temperature and light sensors and their connections to the Arduino
-Ensuring the temperature sensor accurately measures temperature in water
-Setting up a serial port connection between the Arduino and my computer
-Calibrating the food dispenser so it does not over- or under-feed

Potential improvements (if I can get it working in general):
-A stand-alone user interface
-PH, Nitrate, Nitrite, Water-hardness, and Alkalinity/Buffering Capacity sensors
-Small-volume liquid dispensers for automated regulation of more chemicals

Any advice, speculation of problems I may run into, or resources you can share would be appreciated, or if you just want to talk about this project or something, feel free to post.

Thanks and best regards!
-Joe