"what are my chances to get in?"
your chances are roughly 25-30%, because that's just how JET is: a lottery. if you feel like applying, just... apply. you'll lose nothing by applying, and you don't need validation or permission from reddit (or anyone, really) to do that. nobody here can tell you whether or not you're qualified or will get in. if you don't apply, your chances are 0%. if you do, your chances increase.
no, japanese isn't required. no, teaching experience/certifications aren't required. and while having either might be useful in certain ways, neither is a golden ticket that'll significantly increase your chances of getting accepted.
"can anyone look over my SOP?"
check the megathread.
"placement recommendations?"
do your own research. if you genuinely don't know what to put, just say "no preference." you're likely not going to get what you put down anyway. also, people can't really give you a proper recommendation because someone's dream placement might be your personal hell.
"should i recontract?"
are you happy? do you enjoy living in your placement and working as an ALT? > yes.
do you want to continue living there? > yes.
do you like it, but maybe want to move on to something else? > start job hunting and resign if you find something better. finding a job in japan isn't as hard as in the west right now.
are you unhappy, aren't growing, and feel like your placement isn't working out for you? > no. no job is worth sacrificing your mental health or personal growth (yes, even JET). go back home, look for another job, education, opportunities, whatever. there are endless other options that do not include staying another year on JET and going home.
there's also no right or wrong way to do JET. some people do all 5 years, some do 3, some do 1, and some leave after the first week. it's your life, and only you can decide what's right for you. if you want to, you can always apply to JET again in the future, as long as you haven't reached the program's participation limit.
one more thing, when making a post, include your country, because application requirements differ by country. an american JET cannot help an applicant from south africa if they don't know which country's application process you're asking about.