I believe the maximum you can enter is 30? Or slightly higher, but I definitely remember someone on the forum not being able to enter all their travel history.
I would pick the longest duration + first-time visits first. Leave out any subsequent (or transit) visits, but explain it in the LOE and attach your Excel spreadsheet to the LOE. You can probably figure which visits are more interesting to them - a lengthy trip to the Middle East is more important to mention than the 8th visit to Sweden.