Do You Need an IDE to Develop Android Apps?

1. Signing the app I would generate a separate key for the company, and sign it yourself. The other company doesn't sound like it's at a technical level to appreciate the importance of a private. Also, I'm not sure what your agreement is, but they could at a later date ask for the keys used to sign the app they are selling. If you sign it with your own key, that means they could potentially sign other apps with your key and market them, something I'm not sure you want. If you're fine with sending the sources to the other company (with all the associated support costs of helping them set up a development system), it's a good option.

2. Licensing See above. If you have their key, you can sign apps as the other company, something they might not be ok with. Having each company handle their own keys presents the least potential for conflict.

3. Publishing This is the area where I'm least familiar with. I guess the answer would depend on your relationship - is this a one-off or the first of many? If it's a one-off, and you have a good relationship, you could ask for temporary access and do it yourselves; if you envision further work down the road, going through the pain of teaching them would make it much easier down the road.

Hope that helps!

About databases, Android applications use SQLite natively. So if you need local storage you can just use it.

Applications that need to sync with an external database probably cache a number of query results and re-do the queries when needed, since it's uncommon you need the whole database locally (do yo make a local copy of a website database each and every time you use a web application inside your browser?)

For example, Twitter queries the central server when needed and keeps a cache of past tweets.

About credentials, roughly speaking every application you install creates its own user, so it doesn't really need to know any login credential, because it can use only its own user. Think of it as a kind of sudo.