Now that the Obama Administration has decided to start providing US arms to the Syrian rebels, the logistics are already worked out. They’ve been funneling arms from other nations to the rebels for over a year now. The big change will just be where the arms came from.
That and the vetting process: the US mostly looked the other way as arms from the GCC nations and others got shared around the Syrian rebel factions, starting with more palatable groups and ending up with everyone else, including the al-Qaeda allied Jabhat al-Nusra.
Having US arms show up in the hands of al-Qaeda fighters is an embarrassment the administration would prefer to avoid, and that’s going to mean creating some much more stringent vetting strategies.
That’s going to complicate things, with large swathes of the rebellion at least nominally al-Qaeda-linked. The decision to arm the rebels was primarily about keeping the civil war going in the face of recent gains by government forces, and that means providing aid to a trivially small faction in the rebellion that can realistically be “trusted” will run counter to that, meaning there is going to be intense debate on the standards to be used.
Even when they settle on this, the problem of organization is going to be huge. The US has been struggling with pledged cash transfers to the rebels because they are so disorganized, and can’t tell who the “leadership” realistically is. Those problems aren’t going to go away with the introduction of US arms, and in many ways that may complicate the matter, as different factions try to create the illusion of being in charge in the hopes of securing advanced US armaments.