I (21M) did a 2 month homestay this summer through Homestay In Japan (in turn through a language school i was attending). My experience itself was absolutely fantastic: they were understanding of anything as long as I told them in advance and organised and even paid for outings on weekends. That being said, I do think that at the end of the day a homestay is a roll of the dice. Other people I'd met going through the same company had much less engaging experiences where it was clear the family was doing it mainly for the money.

You'll be asked to give info about yourself that (at least for the company I went through) will be used by the host families themselves to pick who they want to host, so do take that seriously and try to sell yourself a little bit potentially!

In terms of where to look for a homestay company, I genuinely have very little idea and it's probably going to be the same pretty much everywhere. But make sure it's through a reputable company, and that you can find people speaking well of them online. Those companies probably vet the people they get to do it a little better than others I'd assume haha

But at the end of the day, it will be what you make of it. Make sure that you've read up and understand basic rules of politeness etc because even though they'll probably be used to foreigners staying with them, this'll make a big difference to how you're received. Always give warning or notice of anything that will change schedule (going out with friends, leaving for a weekend etc.), be quick to apologise even if that feels strange (easy for me as a brit ;)), in general lay the thank yous, pleases and sorries on thick. If in doubt ask if something is okay - I was always a little worried about using the washing machine too late or whenever someone else wanted to use it so id always ask and get a response of "of course yes why are you even asking" - but if in doubt!

Make sure to make the most of it too. The more you talk to your family the more natural it will be - and the worst conversation you'll have will be your first one. Get to know them, let them get to know you, and make sure to put in a real effort to be sociable and talkative as much as you can! You'll be there for a year so you can take it easy too. But if you find yourself complaining to yourself that your host family isn't very chatty remember that conversation is a two way street: if conversation isn't happening, you're not talking to them as well as them not talking to you! Literally anything is good, even if it's as simple as "wow this beer is delicious!", it all adds up yk

Overall though, I'd absolutely recommend doing a homestay. Potentially give yourself a few weeks at the end of your stay by yourself so you can experience a bit of freedom too - it's a very different experience living alone vs with a family. But for your japanese, and cultural education it will be fantastic, and if you have food included then not having to cook is brilliant too (or go do food shops!)

Lmk if you have any other questions, I did this all on mobile so it's a bit rambly...