I'm currently getting my Manuscript professionally edited. I'm starting to sway more toward self publishing and I'm currently doing my due-diligence. However I think I would get great value from at least hearing what an agent has to say. I've prepared a cover letter which is 500 words, is that too long?
The format goes something like this:-
1) I have completed a novel of 100,000 words...
2) The central concept is...
3) The genre is Science Fiction set in....
4) I think my audience is....
5) The story is about...
6) I enclose the first three chapters...
7) About me...
8) I've chosen you as an agent because...
If it fits on one page, which is should. I see no problem as long as it has all of the points you've mentioned.