Magneplanars are dipoles, aren't they? I think that lack of deep bass would be the biggest shortcoming - corrected by adding a sub at some point. If you like the sound of planar speakers, you might want to check out Martin-Logans, which are electrostatics for the highs and mid-range, but use conventional woofers in the bottom of the cabinet for better bass response. They also make timbre-matched center channels for later.
Quad electrostatics would be too expensive, unless you can find some used ones cheap. (I have heard a little bit about a new, cheaper line of Quad speakers, but my impression is that they aren't electrostatics, and bear little resemblance to "regular" Quads. That is not to say that they don't sound very nice - just that they are a distinct design departure from electrostatic Quads.)