I went from a D30 to 40D to 5D3. My goal was to get the FF aspect and IQ. I have used the 5D2 borrowed for about 5000+ shots (landscape and portraits). 5D2 is enough for anyone not doing professional stuff. For a good while. I just could afford the Mark III, that's all.
Weight is not a big deal when you pay such a low price for a FF camera with "contemporary" IQ (I mean the Mark III did not really improve much on that part

).
Flash: get some cheaper chinese flashes, they are probably not as good as good as original but might do the job for you until you overgrow them, or a 430.
Biggest deal on an FF are the LENSES ! This is expensive! Don't buy the kit lens - have you been happy with the Rebels kit lens? For how long? If yes, OK, go for it. The Mark 2 shines really with good lenses (Canon or alternatives, not going to discuss this here). But consider this: if you buy the 5D2 now what will be your next DSLR in about 5-7 years? What will be it's IQ? Think future - get the best possible lens you can afford (faster than f/4!) , if no zoom, no big deal, get a prime. For weight reasons a bought not a 70-200/2.8 but a 135/2. Cheaper too. So, ask yourself if you could go with let's say a 50 and a 135 for a start. If you need wider - go stitching.
Good luck!