Detecting address labels using Tensorflow Object Detection API
It is difficult to say whether the algorithm will detect full box of text or not. This is kind of difficult problem because object to detect does not have proper structure. I might be wrong here!

You are labeling correctly.

You have very few images to learn from. More images are always better for learning tasks.

Don't look at loss value which appears in the terminal, instated check total loss in TensorBoard (I am sure this loss will be more).
For how long to train? in the example config file from TensorFlow API they say on pets dataset (which has only 7349 images) you need to train model for 200000 steps to get satisfactory results. If this problem is learnable, training for more steps should work.