Make sure you are not indenting your code with TAB characters. (The example you have here uses tabs instead of spaces.)

As far as ini file goes, You can write as many sections as you want - just not in one line.
There is nothing that stops you using multiple /writeini commands in one alias.
Code:
/writeini file section1 item1 value1
/writeini file section2 item1 value1
/writeini file section2 item2 value2

You can't have subsections in inifile though, and it looks like you are trying to achieve that.
You could however go for different route and have one ini file per channel or have a section with name such as #Michaelukz-BanList

echo -a $signature