"Do you want noodles or rice?"
想 means "would like to", which expresses wants.
要 literally means "to want", which has stronger stress of desire than 想.
想要 also means "to want", but it also means "to desire". This is used in wide range of extent, which can depend on the context brought up.
Here is the article for further explanation.
Pretty much, yeah. Most Chinese words are more than one character long. People would know what you meant but it wouldn’t sound exactly right.