It is certainly possible to load more source fields than 45, I just tried it with csv and txt and in both cases all my source file fields made it to the READ data structure.
Reading from the source file has nothing to do with the recording.
Steps 2, 3, 7 and 8 are basis for reading
step 1, 4, 5 and 9 of LSMW are basis for conversion.
Can you post a screenshot of your step 7