I didn't add the references because I got the info from many different websites but here are the references for the ones that pctjunkie listed.
Most islands: (I got this answer wrong because I looked at the website wrong. The answer is Sweden) https://www.worldatlas.com/articles/which-country-has-the-most-islands.html
Technically Sweden has the most amount of islands.
Also Japan is a dubious answer for lowest elevation (assuming you were including undersea trenches)? Lowest dry land elevation would be the better question :)
Most islands: (I got this answer wrong because I looked at the website wrong. The answer is Sweden) https://www.worldatlas.com/articles/which-country-has-the-most-islands.html
Poorest: https://www.focus-economics.com/blog/the-poorest-countries-in-the-world.
Lowest elevation point: Japan because of the mariana trench.
Also Japan is a dubious answer for lowest elevation (assuming you were including undersea trenches)? Lowest dry land elevation would be the better question :)