Should probs be てつだって really, as that's supposed to be more for helping out with more minor stuff, たすけって more for when you're dying etc. (or need urgent assistance)
For genkoo yoshi though, if you're addressing someone, should be ____ さんへ
and when you sign off ______ より
Start it off with 2 blocks down from the first verticle line, then when you go to the next paragraph, just one block down.
Full stops go in seperate box(top right), except if it's the last box of a line, in that case it just goes in the top corner of the last character of the line.
And of course, top to bottom, right to left.