If I know what words/concepts Chinese characters represent can I understand a written text without knowing how to speak the language? Could Chinese characters be used to spell English words for example?

I don't know if I get your point, but...are these what you want? 四大发明 star farming 狗 go 币 be .... Actually, when I was in my grade seven, I began to learn English and I, like a lot of classmates, used Chinese characters to help me remember the pronunciations of new English words. For example... Thank you 三克油 How do you do? 好度有度 Hope you've got some interesting informations.

Of course Chinese characters can be used to write English. Here is a modest proposal for it: http://www.zompist.com/yingzi/yingzi.htm

Yes, why not, Koreans, Japanese and Vietnamese managed to use Chinese characters to write their languages, which were originally as remote from Chinese as English is, be it from a phonetic or grammatical point of view.

Theoretically yes, you can understand a written text without knowing how to speak Chinese. In the first decades of 20th century there was a national debate in China on which should be the standard of Madarin, Cantonese or Beijing dialect, and as we know at last Beijing dialect prevailed. Participators of the debate communicated via written articles on news paper.  But even today if you can find a person who can speak only Cantonese and a person who can speak only Mandarin, you will also find that they can not communicate with each other orally. So as long as you can mark every character and every word with the right meaning and are skilled with the written grammer, you can communicate with every Chinese via written texts.

No. Chinese characters was created so that Chinese from different region who speak different dialect and accent could all understand each other. You have to know to speak one dialect. So you can't do it inversely.