First of all, Textpad is an amazing editor! Really!!
But do you know if it is possible to save the size of the "Open file(s)" window? I don't think because it's a standard window but you know...
What I would like to see is a way for that window remember its previous settings. It always (for me, at any rate) opens in List mode. Often I will switch to Details mode, and sort by time (since I'm looking for recently modified files). The next time I open this dialog, it's back to List.