Not quite. A chest plate can make it hard to observe if the xiphoid process has been pushed in and fractured. The AP plate is usually used for bed-ridden patients as it provides less resolution and some parallax distortion due to the short distance between the X-Ray source and detector. 

Not quite. A chest plate can make it hard to observe if the xiphoid process has been pushed in and fractured. The PA plate is the standard plate providing the best resolution/detail, but even then seeing the xiphoid process against the shadows of mediastinal/vetebral structures at the midline is very difficult.

Correct! An X-Ray is good choice, low cost and readily available. The lateral view is the most useful for observing if the xiphoid process has been pushed in and fractured, but a small fracture may be hard to see and a diagnostic method with higher resolution is likely to be needed.

Correct!. A CT scan is a great choice for providing additional or more detailed information compared to a simple chest plate. In a facility with ready access to a CT scanner it may even be your first choice over the chest plate. The negative is a slightly higher radiation dose and potential cost to the patient of the more expensive scan. 

Incorrect. MRI is not very good at visualizing bone tissue (but is superlative at soft tissue anatomy and pathology detail). 

Incorrect. Ultrasound is not very good at visualizing bone due to the acoustic shadows cast behind the bone and generally low resolution of the modality. It would be very difficult to visualize a defect such as a fracture.

Incorrect. With modern diagnostic imaging the value or need for exploratory surgery is greatly reduced. Indeed, there are very few conditions where such an approach is used these days.

Correct! The typical patient work-up should include a history and a physical examination (the H&P). A good physical examination allows you to assess the extent of the patients pain and may yield details the patient has not articulated.