That's been my experience too. 7+ years in industry and lot more before, and I now finally feel like I have more time to do fun side projects. Some may say it is all about the journey, but i rather build for whoever is going to use it, even though it might only be for myself.
I see, so about 900 symbols per 30 minutes. IEX puts out one file per trading day with every trade on IEX, so you get the last trade for about 8,5k US symbols in one download the next day ~12GB compressed though. Has Yahoo ever throttled you at that rate?
Very cool! Where do you get the market data from? I am building something with financial data as well, and couldn't find any inexpensive source I was allowed to republish, so I ended up using IEX.
It also depends on what you are building, and who you are building for. Are most of your users or customers worry about data sovereignty? Will they be in the future? CF is a good and easy service until you need something else, if you go for a lock-in vendor, preferably you should atleast have some idea how to migrate off the choosen platform.