Welcome.

As for the memory card, there's no reason to insert it before reflashing. You do need to decide whether it's going in the internal slot or the external slot. The only difference is the the control panel applet only will put the swap file on an internal card. You can easily change your mind later.

The non-preinstalled application I use the most is mplayer. In my opinion, it's the only video player worth using. You should be able to install it from maemo.org