Concrete Footings for 16x24 log cabin
I use the extreme cases when preparing footings, the map I looked at showed 36” would be an extreme condition and as such constant frost heave at that depth will not be a problem. As far as your piling I have done quite a few homes and never shaped the bottom other than flat, if using a auger to drill your holes they do end up with a bit of a point.
I usually put a couple shovels full of rock in the hole so the concrete doesn’t mix with dirt as it is pumped/ dumped in the tube, code in my area requires the piling to be 6” above grade, small diameter piling (less than 18”) also require tubes to prevent dirt contamination and a 5000 psi mix .