None of us have the right to say what you should or shouldn't do with your own story. Anyway, Vending Machine In Another World is too similar to a Japanese novel, already been translated on Novelupdates for the past 5 years. With that title, you're gonna get a lot of accusations of plagiarism and hate-comments eventually.
https://www.novelupdates.com/series/i-reincarnated-into-a-vending-machine/
Try to change the title or the story a little bit. Something along the lines of 'Vending Machine of Doom' (where the vending machine dispenses addictive sugary sodas that eventually cause everyone to die from diabetes) or 'The Heroic Vending Machine Mecha' (where the vending machine can transform into a giant monster-beating gundam) or 'Vending Machines Need Love Too!' (a smut where girls make love to vending machines). Otherwise, you will be accused of plagiarism. Whether it really is plagiarism or not, the person accusing you wouldn't care. They probably wouldn't even read the story.
As for whether or not to make it a harem, that's up to you. Ai-chan has heard people saying they hate harem, and there are also people who said they look for harem and some others don't care at all. It's all up to what kind of people you want to be your fans.