Calculating homemade yogurt’s fat

The answer is that they are not much different.

During fermentation, some of the milk's lactose is converted by bacteria into protein and other substances. The amount of conversion is pretty insignificant in terms of calories and grams of macronutrients. The most important effects are the changes in taste and consistency and the presence of live bacteria. Usually many of the bacteria survive the highly acid stomach fluids to reach the small intestine where they continue digesting lactose.

Fitday.com gives the info below for a cup of each, which may be surprising at first. However, commercial yogurt tends to be more dense than milk, as you might see if you make it at home: a cup of milk gives you some watery fluid floating on top of less than a cup of yogurt.

Food              | Calories | Fat  | Carbohydrates | Protein
------------------+----------+------+---------------+--------
Whole Milk Yogurt | 149 kcal | 8.0g | 11.4g         | 8.5g
Whole Milk        | 146 kcal | 7.9g | 11.0g         | 7.9g

To answer part 1. I recently watched the Chicken Tikka Masala episode from Blumethals "Further Adventures in Search of Perfection". The recipe calls for marinading the chicken for quite a long time. A transcribed recipe says 10 hours: http://www.dominicsayers.com/documents/ChickenTikkaMasala.pdf.

They also go on to compare the results of a yogurt marinade and a yogurt-less marinade on chicken under an MRI scanner. I don't know if this is valid, but the yogurt apparently had an effect.