Not difficult at all. Most quant dev position require you to be decent at coding in either python/JavaScript or C#. If they see you have that capability, you can land an interview at least. They do require coming into office though.
Quantitative hedge fund. They pay well and depending on what desk (What the team is trading) you end up joining, the environment is in between corporate and startup.
Most cases when a company shares the codebase it's to give you freedom to explore what you'll be working with while they decide what specifics tasks you'll be undertaking.
Get your dev space up and running and play around with stuff you read in available docs.