Advice needed - Beginner who wants to teach themselves.

Background story:

My former business partner was the one managing my finances as they are an asset manager. He did incredibly well and I have made profit since BTC is still on the rise.

Since we've stopped working together, I'm still investing with them until the end of our contract. I'm not sure they will want to keep me as a client so I would like to teach myself.

I have a lot of questions: - How do you know which currencies are worth investing in? - When do you sell - I'm assuming it's best to keep everything long-term. - Is Coinbase the best place to invest? - How can I limit my losses? - Are there other asset managers that could perhaps take me on as a client - where can I find them?