For number one, yes, but make sure you are looking at the frequency in ppm when you multiply by the spectrometer frequency. For most spectrometers you can also have the chemical shift displayed in Hz, in which case you can just calculate the difference between the two signals. This is more accurate because the ppm value is usually rounded to a tenth or hundreth of a ppm, which becomes significant when you multiply by 400!
For number three, do you really mean a doublet of doublets, or do you mean a quartet? For a quartet (a resonance split by three other equivalent nuclei) there would be only on J value. For a doublet of doublets, you would have two, as you indicated in the image.