1. Czechia is probably forced to be closer to Germany, especially in a no-Habsburg scenario. It also will probably have to give more to the Sudeten Germans, both because Hungary shows peaceful coexistence can be had and because the Germans are at that point a large minority.
The Germans would constitute about 30% of the population of this Czechia. Could they have a strong enough political weight to make the country officially adopt bilingualism? Or is territorial autonomy more likely? Perhaps neither of them are on the table? Czechs would still have a supermajority (~69%) in the population, after all.
2. Germany would probably go for Czechia first, unless the Sudeten Germans are so happy they don't want out. Now that would be an interesting factor...
Even before Austria?
But yeah, if the Sudeten Germans are largely content with their overall situation or atleast are visibly split over the issue of secession, then that would certainly put a big wrench in the Nazi plans and damage their narrative. I wonder how this would influence the stances taken by the Great Powers (at Munich)? Maybe Germany would invade if the talks fail? Would that mean an early WW2? Or would the Czechs get abandoned (to buy time)? How well could the Czechs do against Germany? I assume Czechia might give up on Zaolzie in such scenario to buy Polish neutrality.
3. Leaning no, because Hungary doesn't have anything to gain there, unless they also happen to be led by some far-sighted mastermind who correctly understands collective defense as a necessity.
You're right, I think. I was thinking that the ethnic nationalism-fueled policies of Germany would be seen antithetical to the new multiethnic political structure of Hungary, which would make them be perceived as a direct threat to national security. But yeah, the OTL Polish attitude taken during the Sudeten Crisis greatly highlights how shortsighted and/or ignorant country leaders can be in such situations.
At that point I also doubt Hungary would be that weak, as it's got a decent population and economy.
To some degree, yes, but the military restrictions of the peace treaty would certainly make itself felt (even if the Hungarians try to cheat it through the years). I guess it would be either the Anschluss or the Sudeten Crisis which would at last trigger the renouncement of the restrictions placed on the country (maybe unilaterally).
4. Yes, assuming a defensive pact is on, it would be invoked on the case of a German assault unless it's specifically worded not to.
Perhaps there could be a clause that ties direct Hungarian involvement to some conditions. What could those conditions be? Anglo-French involvement? Full Polish mobilisation? Poland being able to stop the initial German attack? Polish troops on Hungarian soil? Guaranteed Romanian and/or Yugoslav neutrality? What are some realistic options?
If Hungary does in fact join the war on the Polish side, how could that influence the course of the campaign?
Assuming the points in (3) to be true, then Germany would definitely try to bring Romania on board with promises of land, potentially calling in Yugoslavia
I believe that to be the case as well.
potentially calling in Yugoslavia, potentially bringing in Italy
If Yugoslavia gets involved by this point, it would be probably on the German side. Even if they have normal relations with Hungary, going to war without any direct benefits (but with many risks) is probably unlikely on their part. German-allied Yugoslavia however brings into question Italy's stance.
5. A Sweden is impossible, even in its wanked state the country is neither powerful enough nor isolated enough to be worth ignoring. Assuming the Axis camp is the same (and I think chances are, things go differently at least to a degree), then it gets pressured under threat of dissolution much like Yugoslavia, with the same potential fate (if refused, then it gets invaded and partitioned).
If Hungary stays out of the conflict until that point, then maybe it could join the Tripartite pact and allow German military transit, but maybe it could stay out of both the Yugoslav campaign and also the initial invasion of the Soviet Union. Of course, the pressure to send troops against the Soviets would keep increasing. The country either commits against the Soviets or get invaded by the Axis? How long could the decision be put off though?
6. Not much, the main problem of this Hungary is that while it does have a couple good allies, they come with liabilities; the Yugoslav one is manageable overall, the Polish one far less, but in either case, as soon as one European conflict starts, the chances of Hungary being dragged in the chaos and losing a piece here or there grow dramatically.
With this I agree.