so i bought a scope online.

is your front sight your gas block? because if yes, then yes.

You can also get a mount setup to co-witness.
What is the scope? What magnification?

My 20" has a fixed front site that I look right through.. At high power it doesn't really show up in my field of view. When I'm shooting out from 50yrds-300+ I don't really see the front site even though it's there.

slap it on there and see what it looks like when your looking downrange

No you do not need a riser to go over the front sight.

Anything over about 3x you can see "though" the post. Not sure exactly how it works but you wont even see it.