It's a very complicated Sugya from many angles.
Yup. i spent way too much time going crazy on this. I'm going for pesach and im going to keep 2 days (obviously if there is any sort of possible emergency/someone in slight danger i will break it faster than u can say havdalah on yom kippur). there is no simple answer. I lived in sha'arei chessed for a while and always kept extra days, and heard from many people there how r Slomo Zalman was strongly opposed to the 2nd day minyanim with people saying brachos that really make no sense in israel and against the minhag of the community, and without a clear source in chazal that the application of the 2 day custom should apply when actually being in israel (note that in the time of the bm, no visitors/oleh regel kept a second day/brought second day karbanos, yet here we are prattling about this and that musaf...). Moreover, while there are few possible real instances of a possible Ba'al Toseif breach, eating matzah and no chametz on the 8th day is one of the few cases where it really looks like it should be an issue, and at the very least is avak ba'al toseif
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that said, there is a lot of firepower backing the need to be machmir and not be over on yom tov restrictions either that i just dont want to mess with (though there are recent big poskim like R Melamed that would rule for many visitors who have strong connections (spent a lot of time in israel already and will spend more) that its ok). its like a tightrope. i will daven in a big minyan, but i will fill really awkward about it. S’iz shver tzu zein a Yid, especially a galus yid.