Challenge Eight - first clue

This looks strange but it seems to be a reasonably standard ADFGVX cipher, using the characters S,U,E,V,I,C instead! Also, we know that Aggie has a habit of reading across the rows not down the columns in the transposition stage of the cipher. Your task is big.

Step 1. Guess the keyword length - another clue about this later
Step 2. Figure out how to transpose the columns. This is really tricky, but there is a way of cutting down the possibilities. The columns come in pairs, and if you can figure out which ones to pair together that cuts the possibilities a lot. To find out pair them all the ways you can and in each case do a frequency analysis to see what distribution of pairs you get. If column x pairs with column y then the frequency distribution will be rougher for that pairing than for any pairing x with another column. Start by trying to figure out which column pairs with column 1 then try to find a second pair from the other columns and so on. I used Excel to do this.
Step 3. Once you know how to pair the columns you need to work out for each pair which order they come in, so knowing that colummn x and column y are paired you need to know whether to write the pairs in the order xy or yx. To find out do a frequency analysis of occurences of the 36 letter pairs for each choice (xy and yx) for each of your pairs. You want to choose the ordering so that you get roughly the same frequencies for all the pairings.
Step 4. Once you have done this you have reduced the transposition stage from 2n columns of individual letters to n columns of letter pairs. There will be n! ways to rearrange the columns and each rearrangement can be viewed as a simple subsitution cipher. Of course only one of them will give you the answer, so you need to examine each one in turn and try frequency analysis. With some effort you will crack the cipher.

I will give more clues as time goes on.