Well . . .
. . . I'm probably least qualified, but - where are you "uploading" the orders? And, the question "how orders are exported from Ecart and in what file format" is actually a hidden passing of info between your website & the payment gateway (PayPal, etc.).
If you're using Dreamweaver to build the HTML pages, the field character limit details are described by the "Properties" panel. The Display Manager or Checkout Wizard functions in eCart will build Forms with default field/column widths (override with the DW Properties panel or CSS tweaks).
Otherwise, if you're referring to "validation" for input restrictions, I believe WebAssist's Validation Toolkit is effective (or Spry) . . .
But again, I'm probably not addressing your question. Luckily, there are some very helpful folks here . . .