... with a long cage Tiagra rear derailleur.
I don't think the Tiagra rear derailleur will handle a 32 tooth cassette
crank in the B screw and give it a try.. even a 12 - 28
will give you a 4:1 high & a 1:1 low gear..
drop the 28 to 24t on the front ,
and then when you go out of state, to the places further from sealevel,
then your mountain climbing extra teeth on the back, will be that much lower.