You mentioned developer APIs. I did work on a match server using QuickFIX a while back and did some work with GDAX apis over Christmas. It was a dead cat bounce because the quick fix web site is down pending domain renewal - for one. Also got connected using rest API in the sandbox, but not using actual login signatures.
I am able with a little more work to get price history and do analysis, etc., but it appears Coinigy already is doing a lot of that functionality already. So I'm not sure if there is much point in pursuing code any further, but it was kind of fun tinkering with it.
If you have any ideas for turning your trading skills into code, I would be interested in hearing about it.