Is it correct to say "Al-Isra wal-Mi'raj" (the Night Journey and the Ascension) or "Al-Isra wal-Uruj" (the Night Journey and the Ascent), and is there any issue in combining "Al-Isra" as a verbal noun with "Al-Mi'raj" as an instrumental noun?

The original (and preferred) phrasing is "al-Isra' wal-Mi'raj" (الإسراء والمعراج) because this is the usage that scholars have consistently adopted. "Al-Mi'raj" (المعراج) with a kasra on the letter meem, is the more common and correct term. It means "ladder" or "ascension device," and it is a noun denoting an instrument. As for "al-Urooj" (العروج) with a damma on the letter meem, it is a verbal noun (masdar). It is recommended to use the common and established term "Laylat al-Isra' wal-Mi'raj" (ليلة الإسراء والمعراج) rather than "Laylat al-Isra' wal-Urooj" (ليلة الإسراء والعروج).