I think your ideas on speeds and feeds are okay.
I'm not sure how much room you have for your tool to work, but I would probably rough the area with an ordinary straight endmill first, cutting to the profile outline at the bottom of the stock.
Then, I would make a series of offset paths for the tapered endmill at full depth. The effect would be that the heavier upper section of the tapered flutes would be cutting first. Using the calculator, I would determine how much offset of the profile would be required to cut about the first .125" depth, then for .25" depth and finally for full depth. The depth of cutter engagement would increase for each successive pass.
If chatter becomes a problem, I would go back and create intermediate profile offsets that would allow the tip of the tool to cut the final profile, but at only 50% depth into the material, followed by another pass (using a different offset profile) at full depth.