first of all hi and welcome to the forum
No there are no different species of corns. Those are genetic mutations (often first found in the wild) that are bred so that the snake keeps that mutation. I won't give you a genetic course there is a forum for that and i might mislead you. But to get back back to the question : an amelanistic corn (often called albino because it lack melanin) is still a corn snake, an anerilistic (one that lacks all red pigment, sorry for the spelling) is still a cornsnake, now the fun part is when you combine those 2 genes you get a corn with no red and no black, those are called snow corns. So thats where a lot of color comes from, they are wild cought then mixed togheter with plenty of other color that already exist, it's a little more complicated but i'll let you read in the genetic forum if you need more explanation.
As for pattern there are 3 basic pattern (Normal, motley(rounds) and stripe(2 stripe all the lenght of the snake)), 1 that we don't quite understand the genetic (aztec/zig-zag) and a mix of motley and stripe called motley-striped (tser are weird, some have X pattern, some have some weird unconsistent stripe). The genetic behind the pattern is similar to the color but there are some differnces
All corn have the same scientific name the is
Elaphe guttata guttata (i'm not sure about the spelling) no matter what the color or pattern is. They are all the same species the thing that changes is the Morph (Amel, ener, motley, lavender, hypo, etc ...)
usally corns get about 4-5 feets going from 3 feet to a max of 6 feets, personnally i only have a juvenile corn of 2 feets
I dont think that the size of the male differs from the size of the female ... maybe the female gets a little bigger but i don't know since i only have a juveline male ...
Except for breeding purpose i don't think the male or female changes anything, they are both very docile and like to be handled
For the good site on corns where you can ask newbie question, well your on one
Ask ANYTHING you want here there will always be someone to answer even if the question seems stupid ! By the way before asking you might want to try to do a search on the forums on the question you have maybe someone already posted it.
it's a good thing you get "The corn snake manual" everybody says it's good, too bad i haven't someone that sells it near me
Have fun with your future snake !