He's doing landscapes. 7d with 24-105 might be too tight unless he wants to try panorama.
That's correct, that's why I bought what I've got now - 60d + the very reasonably priced 17-40L is ok for landscapes, and it's a full frame upgrade path unlike an ef-s lens.
the 6d is a beast in low light so being limited to f4 shouldn't hurt too bad
... except if you're shooting high dynamic range scenes, because less iso noise on the 6d cannot repair the fact that dr takes a hit also on the 6d, though not as bad as the crop sensor: http://www.sensorgen.info/CanonEOS_6D.html
DR is gonna be an issue either way, and if the DR in the scene is too much then bracketing the shot will have to happen (or get some grad ND filters...)
Note that in my original reply, not making a judgement based on the OP buying his first DSLR.
As for first DSLR and lenses --- FF vs crop. each do have their place. Landscape vs lowlight -- again each area is different - and what kind of low light are you talkig ---low light portraits...low light landscapes, low light waterscapes? For low light, a good tripod may be a better investment, unless your shooting people...then even with a good low light body you may still want a flash for fill...
SLR's give you options --- but for limited budget first time investment ---it is almost too many options (due to cost, because each option is pricey!!!!!)
That's why I stick to saying ---if you go FF - get the 24-105. then over the course of the year, check you shots and see what you shoot at the most...if your staying in the 24-35 range and wanting wider - then your in UWA territory. But if you find that your at 105 a lot and cropping, then you may want a 70-200... or, if you find all your shots at 50mm and want more control over DOF and OOF areas, snag a 50mm. This is all stuff you have to find out on your own though, only way to know is have it and shoot. Which is again why I say grab the kit lens ---it may not be the best at everything but it is a great jack of all trades lens (also ---it is L series and L quality so if you do choose to sell it in favor or something more specialized it will retain its value pretty good unless you smash it or something.)