Is a fidyah obligatory for someone who took off the ihram, had sexual intercourse with his wife, and applied perfume after intending 'Umrah and donning the ihram, but before uttering the intention at the Miqat, believing that the ihram is not valid unless the intention is verbally expressed?

Iḥrām is the intention to begin the ritual, and it is not a condition to vocalize the intention; merely having it suffices. Wearing the garments of iḥrām is not equivalent to being in a state of iḥrām unless the intention to begin the ritual is present, as stated by Sheikh Al-Uthaymin. Based on this, what you did, such as removing clothes, applying perfume, and engaging in intercourse before intending iḥrām, is permissible, as you were not yet in a state of iḥrām. A female pilgrim in iḥrām should be mindful that it is not permissible for her to wear a niqāb or gloves. She may cover her face with something other than a niqāb.