Which of the lengths (short, medium or long) are used for a normal 1st and 10? I thought it was medium length, but if so the game is not looking at my gameplanning at all.

It is medium unless you are doing well or poorly and/or have your gameplan adjustment speed set higher. See http://blog.myfootballnow.com/2015/03/short-medium-and-long-what-do-they.html

I'd much rather be able to tell the game what I feel short, medium, and long are(in terms of hard set yardage values) and be able to gameplan around that.

I agree, i would like to be able to decide what i want to call at any time in the game. Maybe in the future?

The reason i ask is, i wanted to run more on first down, so i changed my run % to 80 on first downs. Still during the first half until my rules kicked in, i had 5 throws on first down and 2 runs. I know i am never going to get picture perfect percentages, but unless i have made some mayor screw up in my game planning, then why bother?

You can use rules to have a more detailed control including specific YTG values instead of the short-medium-long controls of the standard gameplanning screen.

This.

Also, if you turn off the in game adjustment, then you know what the static distances are.

What are the standart adjustments for the short, medium and long distances?

Sorry, I am pretty new to this game, and I haven't read anything about those distances anywhere?

Here's the official description:

http://blog.myfootballnow.com/2015/03/short-medium-and-long-what-do-they.html

Thanks!