Just noticed that I had not commented on the number of columns yesterday: There's no limit on the number of columns in FEFLOW. Depending on the format you use, there might be limits in the software you are using to create the files. For example, old versions of Excel only support 256 columns (which used to be quite relevant when working on the dbf tables of shape files in Excel). However, newer versions do not have this limitation (but do no longer allow to save dbf...). To overcome these limits, you can also join several tables in FEFLOW if necessary.