Yes... Welcome to Android or in the larger context Java game development.
There is much to learn and a lot of it falls under the "dark arts" category such that you will have to search and assimilate the appropriate knowledge yourself.
Some general answers to your questions.
is a great resource for Java game development and there is an Android section on that forum.
2) Android 1.5+ is a reasonable target these days and recommended for several reasons such as it's the 1st release to take into account separate resource directories for various screen size and other parameters.
3) You should be able to find this info if you search for it; it's not game dev specific.
4) You need to manage your images as there isn't auto downscaling of images and any auto-scaling features built into Android should be avoided. I suggest looking into OpenGL ES development, but it's a lot to take in as it can make it easier to handle different screen sizes because of the use of projection. IE you work with world coordinates and through projection from a camera perspective/position screen sizes are taken into account. GL ES dev is not for the faint of heart though and you'll have to dig in to learn the details.
I will be releasing a significant framework for real time app / game development for Android covering 2D (Android 2D API) and 3D (OpenGL ES) including a number of tutorials on the subject at http://www.typhon4android.org
, but release is still a month+ away. Bookmark it and check it out soon.
Also start small and verify your work then make something larger. Don't start off creating an epic first game!