I believe Husseini did request that a Holocaust take place...in Palestine.
You may well believe that, but there is no evidence for any such request. Al-Husseini had only one meeting with Hitler, on 28 November 1941, and the record of that meeting does not show him as requesting any action against the Jews settled in Palestine, the only mention of such action coming from Hitler, not from Al-Husseini.
Al-Husseini's main aim at the meeting, something that he kept coming back to, was to obtain from Hitler a public statement of support for Arab independence, which Hitler consistently evaded on the grounds that such a statement would cause trouble with the French.
It is quite likely that Hitler brought up the topic of action against the Jews of Palestine as a diversion from Al-Husseini's request for a declaration of German support for the Arabs, ie along the lines of "I cannot give you a declaration of support for you at the moment, but I promise that I will clear the Jews out of Palestine at some time in the future, but I cannot say exactly when".
It needs to be borne in mind that Hitler saw the Mediterranean area, including North Africa and the Middle East, as Italy's sphere of influence, in which Germany would only intervene if Italy got into trouble in asserting its claims. Such examples of German intervention were the bailing out of Italy in Greece in April 1941, and then in North Africa, both cases where Italy had initiated action but had been defeated.
However, in all those cases where Germany pulled Italy's chestnuts out of the fire, it limited itself to military action, leaving political administration entirely to the Italians. That was because Hitler regarded the commitment of German forces to the Mediterranean theatre as a diversion from the main task of defeating the Soviet Union, and he therefore wanted to keep that commitment to a minimum.
Thus, Hitler's vague suggestion that German forces would cross the Caucasus and invade the Middle East, including Palestine, was most probably not serious. In the case of an Axis victory in North Africa, it is most likely that Palestine would have been left to the Italians to administer, in line with existing practice, which would not have been congenial to the Arabs, since Italy was a colonial power that had a record of suppressing Arab independence in Libya.
It is noteworthy that the only Axis military action against Palestine, an air raid on Tel Aviv fairly early in the war, was mounted by the Italian air force, not the German.
As for Al-Husseini's intentions toward the Jewish colonists in Palestine, there exist letters from him to the German authorities asking them to return the colonist to their places of origin in Europe. The German response was of course negative; having facilitated Jewish emigration to Palestine before the outbreak of war, as a means of getting them out of Germany, the Germans were not going to agree to take them back.