Good mobile SDK design?

I'm a mobile front end developer who's soon to take on the task of developing mobile SDKs for my company. The company is a relatively successful startup in the 'finovate'-sector, providing data-driven services to banks all over the world. While I do know how to develop APIs etc I'm looking for dos and don'ts preferably from experience on developing mobile SDKs. There's already talk in my company of including UI-modules in the SDK, which I oppose since I find it wrong to mix UI and back end data-services in the same SDK...? Further, should we invest energy in developing a shared code-base across platforms...? All advice are welcome.