Some of the checks you are seeking are under the prying aspect on hangers, equal till the root... a inverted hanger is your case. So whenever the bolts and plate thickness are safe in the hanger setup it will be for your plate, but of course you will need to check the fixity one way or another. Welds you can dimension for the particular weld arrangement by Pilkey or other reliable source to size the welds. Then the other more important check is plate capacity for the -if necessary- prying enhanced forces at the bolt points.
How to treat the prying action you can see in the AISC Manual but for not too thick plates some use 125% of the standing tension.
Also, sometimes is more logical to transfer the tension in shear than in bending action. To such purpose you fillet weld fins to the column and bolt down between the fins against the foundation.
In all your design problem also happens for the tensile side of weakly loaded columns where flexion predominates.