Glad you found Eclipse and sensor swabs but sorry you found it the hard way! As you go forward, try just two or three cleanings before taking a break. It becomes an endless cycle of removing some dust and adding more in different places. Often the couple of outlier dust bunnies will fall off once you let the camera sit a bit.
As for testing the cleanliness of your sensor, the exposure TIME does not matter. Just stop down the aperture to f/22 and defocus completely. You can then shoot a clear blue or overcast sky without a flash or instead I use a flash and a white wall...hard to miss the dust spots. Shutter speed won't matter though as the dust bunnies are moving with the sensor.