In the letter they said they disabled it for not enough useful content. THis was a hobby site that had all unique content, but had pages that were undeveloped yet and Im thinking that is why they are said tehre was not enogugh content because the developed pages had a lot of contents

Should I worry about suspension in the near future?

Also I have another site that is all unique but most of the wordpress posts are not that long maybe 100 words, should I be making them longer/?

I tend to go for 300 words minimum per post.

And not enough useful content means you don't usually have enough pages or there is not enough new pages etc.

I've had Adsense disabled on a crappy person blog of mine where I just posted pictures and stupid videos. Still using the same Adsense account for other legit sites with no problem. G just had a problem with the content on the one blog. I wouldn't worry about your whole account if the other sites are up to snuff.

BTW, once you develop the site more and add more content, you can email them and ask to reinstate ad serving on that one site.