Rpi Mods: Customizing UI, Adding New Applications, Etc.

Hello,

I'm new to the Pirate Box, but have been tinkering with the rPi for almost a year now. I have a few questions:

1. What's the best way to go about customizing the UI? I'm proficient in front-end web development, I just need to be pointed in the write direction so I don't break anything.

2. I'd like to add a new application to the server. Preferably a python + flask program. This question is similar to the first one in terms of outlining the general process.

Bonus questions:

Recommend external hard drive (preferably == 1tb) and best way to configure it with Pirate Box rPi.

Recommend way to extend range. I have a small wifi dongle for the rPi, but I'd like to dramatically increase the range. I'm guessing to either connect it to an external router or get a larger wireless antenna. I know a lot of hardware is incompatible so any recommendations would be greatly appreciated.

Thank you so much for any help! I apologize for dumping so many questions in this one post, but I'm attending a hackathon in two weeks and I want to build off of the Pirate Box. I plan on making it off grid/solar powered, but have that covered : )

Thanks again!