All the issues you mentioning has nothing to do with calibration but how you approached the whole process . If that was so easy 3D scanning would be very cheap solution for everybody still it is one of the most expensive services for a reason .
You can achieve better results that in the advertising , but you need to learn first how to use it .
Try using the included model head and turntable , set the gain proper as that is the number 1 issue why you losing tracking , this way you can observe the process better , 3D scanning is not taking a picture , it is time consuming process with a lot of patience . You need to set proper mode for each different object , follow well what you see in the Depth Camera window as that is your guide , make sure the scanned object is always in grayscale , click on Auto and then back to Manual to setup the right gain .
I would recommend you to check the video tutorials for the starters from this forum before get deeper into it as there is lots of stuff to learn about, but most important a lot of practice .
you can see some good results in my thread for inspiration , I am a simple user as you : POP2 - My 3D Models Showcase Progress & Tips - #104 by PopUpTheVolume