Go with MySQL or PostgreSQL. Most of the programmers are savvy with them. This will give time to put your MVP in place and then you can work out a more scalable solution when time comes.
Thats exactly what happens in Brazil. All phones MUST be sold unlocked but they lock you in with contracts in order to get cheaper phones. However if you choose to buy a "fully unlocked" phone, the prices have skyrocketed. (We have the most expensive iPhone worldwide, 16GB 4S = 1.2K dollars).
Most of the Android (and Google's code) is licensed under Apache License V2 which DOES allow proprietary redistribution.
There are portions GPL'd indeed (Kernel for example), but saying that Google should take action on it is over the top to me. If that happened people would start the "GOOGLE IS EVIL AND IS SUING SMALL INDEPENDENT MANUFACTURERS!" mantra for sure.
Android (name and logo) are trademarked by Google and cannot be used without explicit permission. They can however use "for Android".
Also, the Android robot is under CC-BY license. No harm done here.
Early optimization is the root of all evil.