The Arabic q is not pronounced the same as k. The articulation is further back, at the uvula.
The Arabic word *qahwah is not derived from Ethiopic (a related South Semitic language), but from a native Arabic root. Originally it meant ‘wine’, but after it caught on in Arabia, the word was adapted for the new beverage as well. So it could be generalized as ‘a dark-colored strong-flavored beverage with psychoactive properties.’ Arabic did borrow a coffee word from Ethiopic, however: the name for the coffee plant is bun in Ethiopic and bunn in Arabic. No doubt the Bunn company, manufacturer of commercial coffee equipment, will be pleased to know that.
Turkish kahve is simply what happens to Arabic words when adapted to Turkish pronunciation. The letter q has been dropped in modern Turkish spelling, but when written in Ottoman Turkish in the Arabic alphabet, it used the letter qaf. The Arabic vowel a remained “a” in Turkish after a back consonant (like q), but shifted to “e” after a front consonant. Arabic w always becomes “v” in Turkish. The h in the middle of qahwah was actually pronounced with aspiration in Arabic and Turkish, even though followed by a consonant (like the initial /hw-/ sound of English “wh-”).
Italian has no /h/ sound. But the unvoiced h in Turkish kahve went to make the v unvoiced as well, so it became “f” which then rebounded on the adjacent h, making it double “ff”. Italian caffè preserved the accent on the final syllable which is typical of Turkish pronunciation.
Japanese kohi substituted “h” for f. Why? In Japanese, the four sounds [p], [b}, [f], and [h] are all considered, for historical/etymological reasons, variants of the same sound, and are written with the same kana characters. The Japanese [h] and [f] are two allophones of the same phoneme: it sounds like h when it comes before a, e, o; it sounds like f only before u. So English /f/ adapted to nineteenth-century Japanese pronunciation came out [h] if it wasn’t followed by u. Present-day Japanese borrows the [f] sound in any position, but when coffee was borrowed in the 19th century, they hadn’t gotten used to that yet.