1, The "%20" is unicode for a space, if you used a space in the url, it would break the url.
2, As previously stated, they are hoping for the end of this week (http://forum.mfscripts.com/viewtopic.php?f=20&t=1547&start=70#p5610)
3, No, v3.5.3 plugins will not work on v4, they need updating...