Are the martyrs of the Hereafter exclusively in Al-Firdaws Al-A'la, and do they differ in their ranks, and does the reward of one who dies by burning differ from the reward of one who dies by drowning?

Non-martyrs may attain the highest Paradise (Firdaws al-A'la), for the highest Paradise is attained by whomever Allah wills to honor, based on the Prophet's (peace be upon him) saying: "If you ask Allah, ask Him for the highest Paradise." As for the varying ranks of martyrs in the Hereafter, this is not denied, and it is according to the superiority of their deeds and their patience in enduring trials.