I need a 1/4" x 1 1/2" x 80" steel flat bar. I will omit the details of what I need it for because this question is basically asking which composition yields a stronger steel.

www.discountsteel.com has a wide variety of steel bars, but I am not sure how to read the ratings regarding tensil strength and hardness. Here are all the products:

Stainless Steel
Cold Rolled Steel
Hot Rolled Steel

If you click the ASTM material Specifications tab at the bottom of the pages and scroll to the bottom, you will see mechanical data for which I have the following questions:

First off, what is "minimum tensil strength"? The stainless steel 304 has a minimum of 75, but the hot rolled and cold rolled appear to have ranges of 58-80 and 55-70 respectively. Why does stainless have a single number and the others have ranges? Why does it says minimum? Does a higher number mean stronger steel?

What is minimum yield strength?

Second is the hardness scale which uses the Rockwell scale which I've looked into a bit. The stainless rating for 304 is 88, but the rating for hot-rolled is B76. For cold-rolled, it seems to be broken into two: Hot rolled is B67-B80 and cold drawn is B80-B90. This confuses me even more because this looks like the steel is cold rolled hot rolled? Why is the stainless rating just 88 while the others seem to be a range and use the B scale? Does stainless just default to a scale since it's just represented by a raw number?