Try rolling the dice :-)

Your approach is fine. See: http://rais.ornl.gov/tutorials/toxvals.html

Sections 2.3 and 2.4

If you are interested; we have developed a detailed document, which gives procedures for developing toxicity factors and discusses uncertainty factors; see:

http://www.tceq.texas.gov/publications/rg/rg-442.html

Click on the RG-442.pdf file 

You are correct for inhalation. For ingestion see below:

Oral RfD × GI Absorption Factor = RfDabsorbed

Oral Slope Factor/GI Absorption Factor = Slope Factorabsorbed

you are correct. this link can help you.

https://rais.ornl.gov/tutorials/toxvals.html#2.4%20Derivation%20of%20Inhalation%20RfDs%20and%20Slope%20Factors

Yes it is correct!