Fair dos, the only reason I suggested the initial higher boost is as a separation charge, higher thrust initially to get it moving before applying more continuous thrust to gain altitude.
It looks like that would be totally unnecessary with the E6 power curve though as it has a nice peak after about 0.4 seconds and then smooth power delivery after that. The E15 has a bit af a "KABOOM" factor to it which, as you quite rightly pointed out, would put a lot more stress on the structure.
The E6-P definitely looks like a find as well. However, as it has no ejection charge it would appear to be even more suited to single rather than multi stage. Also one less thing to go wrong if there is no stage separation to worry about.
I'm still a bit concerned about the design though. The typical loading of the Skua 1500 looks to be about 300 grams. OK, so the long glide time normally produced isn't needed but the amount of weight required for the GPS etc is probably going to be the best part of a kilo. That loading on that wing section I'd expect to lead to more of a barely controlled plummet rather than a glide back to earth.
Folding the wings as well I'm finding a bit of a stumbling block. I don't dispute the necessity but I can't see how folding them downwards will reduce drag in any way, let alone how to rig an opening mechanism that doesn't either foul the fuselage or add way too much weight. A one or two piece swing wing still looks to be a better bet to me. Have a look at the NAR XP-2C (www.nar.org/competition/plans/pdf/xp-2c.pdf) as that seems to use a more conventional form and is specifically designed for rocket propulsion. Give it a lifting body fuselage above the wing and rocket pod and it might be easier than adapting the skua suitably.