Yes, you could definitely do that, although I'd make sure to keep the poll in a clearly divided section of the page. Once you've received the first couple of suggestions, you could include a poll on the same page. I'd put it on the top, adding a few words to describe what's been selected, that visitors can vote, and so on. Then, below it, you could write something like:
"Would you like to suggest a tutorial that is not up in the poll? Then get your opinion heard and select a topic below!"
Well, obviously it'd have to be written in a more apt way, but you get the idea. Below that you could then always keep your form with topics people can select from and submit to you.
I don't know how well-versed you are in programming your own scripts, but there are a few good form plugins available in the WP rep. [Contact Form 7 comes to mind. It's one of the better form plugins for WP and the plugin's [URL="http://contactform7.com/"]homepage](http://wordpress.org/extend/plugins/contact-form-7/) has lots of documentation available.
As for polls, I don't know of a good poll plugin, but that's because I've never used a poll on a WP site before. I'm sure you'll find something apt there as well.