I agree with advice given above...take the platies back to the LFS and get 5 more tetras. Then you could add a male betta or a dwarf gourami and call it stocked. If the tank is new, you shouldn't really need an algae eater. Chinese Algae eaters get more aggressive with age. I had one that was about 4 inches and sucked on to 2 zebra danios which killed them. They like to eat the slime coat off other fish. Definitely take that guy back...he will eventually cause problems. They also get huge, about 8 inches...I've heard of them getting bigger than that, but have never seen it in person. I've personally seen a 6-7 inch one and it looked huge, so I can just imagine how a bigger would be look.
So you are looking at:
6 Head and Tailights
1 male betta or dwarf gourami
That is a good stocking for a 10g...its not too much, but 10g tanks are small.
Also, head and tailights are not aggressive at all. I have 8 in my 55g that have been with me for over a year (first fish in the tank) and they are kept with angels, other tetras, bolivian ram...and others and I have not seen any aggression. They do like to chase after each other, but hey, what tetras dont do that.
Enjoy the tank!
Articles on the Nitrogen Cycle:
http://www.tropicalfishcentre.co.uk/Cycle.htm
http://www.cichlid-forum.com/articles/cycling.php