Been there, done that as a student with limited funds and I would definitely go with the 70D....
The reason is simple. To outfit a full frame camera properly for sports photography, you will have to spend a lot more money on lenses. For example, with 70D you can pretty effectively use a 300/4 IS lens for a lot of sports, which is a quite handholdable lens. Need a bit more reach? Slap on a 1.4X. In order to have the same reach with a FF camera, you'll need to drop around $10K on a 500/4 IS. Plus you'd better plan on another $1000 to $1500 for a solid tripod and gimbal head. So, $1500 for a handholdable tele? Or more than $10,000 for a tele and a tripod to use it on? Your choice. Similarly, you can use a 70-200/2.8 instead of a 300/2.8. Or you can use a 135/2 instead of a 200/2. All in all, if you need teles for your work a crop sensor camera can be a whole lot cheaper than FF. And your lens kit will be a lot lighter and more portable, as well.
The 70D is perfectly capable of making landscape and architecture shots. Sure, eventually you might want a FF camera for those... but if your "nature" photography is wildlife, 70D is a better choice for that, too. Especially smaller critters, birds, etc. Anything that requires telephotos.
So get the 70D now, and start building your lens kit. It's a bonus the 70D leaves you an extra chunk of money to put toward lenses. The lenses you choose are going to make much more of a difference than the camera you choose, anyway.
You might want to minimize the number of "crop only" lenses you get. But also don't shoot yourself in the foot by not getting necessary crop only lenses, such as an ultrawide for those landscape & architecture shots. The Canon 10-22mm is an excellent lens, for example. If eventually you switch completely over to FF, you won't have any trouble selling off any crop only lenses you might get to use now. (Personally I use both formats and I have two ultrawides and a macro lens that are crop only. All the rest of my lenses are FF capable, so can be used on both).
Eventually you might want to complement the crop camera with a FF camera, perhaps for those landscape and architecture shots. Just don't expect to see a whole lot of difference unless you make big prints - really big prints - from your images. There will be little noticeable difference from, say, 16x24" and smaller. You'll really have a hard time telling any difference between images posted online. The FF cameras do tend to be helpful for low light shooting, often can handle one or two stops lower light. Personally I prefer them for portraiture and some macro, too.
But 70D is quite capable and you should start there, putting more toward your lens kit instead of tying all your money up in the camera body.