Selection of multiple items and then selected one as default

I'm trying to design a web interface in which users pick particular "items" and set one of them as default. The textbox for searching uses autocomplete to find the matching item. I've come up with the following design to allow the user to set the items as default as well as add new items.

Does this make sense from a usability perspective? Should the textbox be on top instead? Do the radio buttons make sense or should it be textual (i.e. "Set as default") or even a combination of both with a tooltip? Should this list scroll if it gets too large or just push other content down?

Additionally, this interface needs to support reordering/deleting items in the list. I was thinking of just dragging the items for reordering. For removing, I was thinking of showing an "X" or "Remove" when an item is hovered over.

If anyone has any better designs for this, I'd greatly appreciate any input.