Taking these one at a time:
Is it ok to have high-level words that some people may not understand right away in a domain name?
It is okay. However, Google really pays attention to the terms you use in your domain name, so try to include one or two keywords directly related to your website in the domain if you can. If you can't, that's okay. I own
elitesouth.com, and you can't really tell anything about my site or services by the name alone... other than where we're located perhaps.
Even though this domain is available, how can I be sure that there isn't already someone using a similar name? Google?
Dont' worry about it. Even if they are using a similar name, they don't have
your name, and that's all that matters. Buy a domain with which you can identify most that contains a keyword or two related to your product or service.
How descriptive should a domian name be?
It's just a domain name. Try to keep it under 18 characters, and you'll be just fine. Read more below.
What is the suggested length of a domain name?
In my domain-buying experience, I've learned that
readability (and the visitor's ability to remember your domain name) is more important the length of your domain name. Meaning, "tonysnewyorkpizza.com" is more favorable (to me) than "nypizzatony.com."
What really matters most is the content you create, the products you sell, and the services you offer. Perfect your content, products, and services, and it'll be much easier for you to market the website.
For anyone reading this post that can't quite think of a domain name (the exact opposite situation of the original poster), poke around on
www.bustaname.com - it's pretty handy and fun.