Chandra Sekaran
Ansys Employee

question 1. There are several types of import convection data samples for film coefficients. I'm curious what the difference is between these.

I believe these are various empirical correlations of temperature vs film coefficients. You can look at the table of temperature vs film coefficient in the xml file located in the directory shown in the dialog

questions 2. Is it correct to set the convection-tabular data-coefficient type to average film temperature to set the air temperature to 70℃ or bulk or difference of surface and bulk temp? Which is best if not both

This really depends on the measurement method I think (what temperature the film coeff was measured at - wall temperature or free stream temperature or some average). 

questions 3. While looking for various information, I think ambient temperature is also likely to be the correct answer, is that correct? If yes, what does step applied mean? If you press the transparent square on the left side of the ambient tempreature, P will appear. What is the difference between this?

The "P" indicates that the value is parameterized. For example you could have some input parameters (say conductivity or film coefficient) parameterized as well as some output quantities parameterized (say temperature at a specific location). Then you can use these parameters in design of experiments/optimization studies.