I am going to base my answer on the way MBC2015 treats irregular key signatures.
I would do the tempo indication exactly as it appears - environs. quarter equals music parenthesis dotted quarter music parenthesis equals 51
The time signatures can be indicated as right and left hand in the music heading - enclose the right hand sign in music parentheses directly before the sharp 12/8. Leave a space, enclose the left hand sign in parentheses directly before the sharp 4/4.
I don't think you'll need to put them in the music line.
(I can't figure out how to use simbraille in this box, so I've attached a pdf. Let me know if it doesn't make its way clearly.)
I also don't think a footnote will be necessary for the meters. It should be clear enough this way. Or are you just referring to the long word expressions?