Thank you all for your advice! To try to answer the questions:
Why not under the top tube or along the seat tube? I like being able to lift and carry my bike from the top tube, annoying having the frame pump there. As for along the seat tube, I would put it there but I want to carry two water bottles.
It is far enough behind my feet to avoid being bumped.
Brake cable: Awaiting trimming once I decide upon stem height/length and brake levers.
I do like both ideas of adding some tape where the head of the pump meets the frame to prevent damage, as well as adding another strap to help hold the pump steady. Another thanks for the voile strap recommendation!
I'll let you all know if/when I perish, after the response of half "yes" and half "no" I feel somewhat confident about trying it out with the 2nd strap.