I dont' think you need to "know" pawn before you start scripting. I think you should just start doing. I suggest starting from
Intro to AMX Mod X Scripting.
Many of the "simple" questions can be answered on one of the pages linked to from
here.
As for source code editing you can choose your favorite plain text editor. I prefer
Notepad++ (
DL Here), it has an a lot of features that make it great for editing scripts. On of my favorites is commenting like 20 lines all at once

(as many or as little as you want).
If you choose to use Notepad++ I have just about all the amx keywords listed and I have a, imo, great syntax highlighting scheme. PM me if you want more info.
Good Luck.
__________________