Sort Text By Character Length, Insert Spaces, Merge Cells

I have multiple columns with many rows of unique text in each. Here is an example of what the 1st few rows of column a and b might look like:

A___________B
hboc______dds
jk________optg
hbv_______pl

FIRST:
I would like to be able to sort the rows by the character length in a column. So, it would look like this (if sorted by 1st column):

A___________B
jk_________optg
hbv________pl
hboc_______dds

Second.........