Your modal analysis looks correct. The only change I would suggest is to use positive values for all the loads when you are doing a modal calculation, as these loads are only used to calculate the masses. A modified file is attached for your reference.
The mode 1 is predominantly a Z direction mode and the frequency corresponding to that is the one you should use for the structure frequency in Z. The mode 12 on the other hand is a significant mode in X direction and you should use the frequency corresponding to that for X direction. The modes and corresponding frequencies are printed in the analysis output file ( ANL file ).
One more thing. There is a user table specification in your file for a channel section. You may want to check the properties you assigned to that as properties like AX, IY, IZ etc. appear to be zero for that section. This analysis is however not affected in any way because of that as you have not used that user table section but just wanted to bring it up.
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