Don't rely on free services for mission-critical aspects of your life. And don't expect free services to provide support.
And no, "it isn't free, you pay with your data" doesn't make it a paid service, it is still free.
Starting on amazon is great, as it really is cheap at small scale, and you can test your shit at large scale for short periods... but it gets expensive fast as you grow, so the more you can do to prepare to move, (or credibly threaten to do same) the better off you are.
And don't put any valuable eggs in a free basket.