Add additional calories on workout days? How many?

It depends on exactly how much exercise you are doing and what kind. An hour of hard running burns a lot more calories than an hour on a stationary bike. Log in your exercise just as you log in your food. MFP will tell you how many additional calories are in your 'budget'. Some people eat half those additional calories. I eat all of them because they are pretty close to correct for me. (I run and walk.) If you start out eating half, and find yourself either really hungry or losing more weight than expected, then eat back more of the calories. If, OTH, you aren't losing as quickly as you expected, then eat fewer of your exercise calories.

I agree with eating around half the calories burned. I try to assess how much I need, by what my body is telling me. Typically I am much hungrier after I do a cardio workout, and try to eat a high protein meal, which is usually what I am craving after I workout for a prolonged period of time. It has worked pretty well for me and I continue to lose. It is a bit of guess work since it is hard for me to tell exactly how many calories I burn, as I do not use a heart rate monitor, so I really rely on how I feel, and if I am craving more protein, I know I need to eat more.

The goal should be to eat back ALL your exercise calories.
The common recommendation to reduce the percentage is (mostly) due to how poor/excessive many of the MFP database entries are.

For your weight training just log entire duration (under cardio section) as strength training - it's not a lot of calories.

For cardio you need to be far more precise than saying "cardio"!
Some cardio it's extremely easy to get a reasonable estimate, for some it's very difficult. And that's why blanket recommendations to eat only a certain percentage really don't make sense on an individual level.
You might be "lucky" and be reducing an excessive estimate towards something more reasonable or you could be reducing a reasonable estimate by half.

Nope.