Re: Another mighty initial thrust idea
(1) the thrust from the rocket will be acting upon the vehicle, not the launch platform: this applies whether it's launched on the ground or in the air. The only issue here is the risk of binding between the aircraft and the launch rod such that energy from the rocket _is_ transferred to the launch platform. The SPB has given a lot of thought to this specific problem though, and remember that the pics from Vulture 1showed little sign of heavy ice build-up.
There _was_ an issue, when the SPB were still planning to use a fairly substantial back 'plate' to hold the cantilevered launch rod which, because the back plate would have an appreciable area, would mean that the thrust from the rocket would act against it. They now recognise this problem though, so now we just have to wait and see how they're going to get around it (personally, I don't think that simply reducing the size of the backplate, to make it much narrower, will be adequate because in the very early stages of rocket burn, when the nozzle is very close to the support, the exhaust jet will be equally narrow and concentrated.
Anyway, it can be argued that a ground launch is more problematic in terms of the rocket exhaust upsetting things because, unless you mount the rocket above a pit to divert the gases away from the immediate launch area, as they do with the big rockets, the gases have nowhere else to go except back up towards the rocket. In a free-air launch though i.e. without a backplate then there's nothing obstructing the exhaust gases from continuing back and away from the rocket.
(2) I'm not sure what aspect of safety you're referring to wrt to the ambient air-pressure. The rocket motor has its own oxidiser, so as long as it can be ignited it's going to burn. Dunno if the low pressure or temps could result in degradation or breakdown of the fuel/oxidiser mix, or ignition issues, but that's what REHAB is for.
I don't know where you got the idea that the launch rod was going to be a "slender wire" - it looked like it was ~8mm diameter to me, and even though Titanium is a little more flexible than steel, at that diameter it's just not going to flex at all.