I'de skip right to FF. You know what it offers, and grabbing more lenses for crop just means you'll end up selling it later.
Consider this, grabbing more glass, your just doing a single upgrade at once, but you go FF, your 50, 35, and 135 all get upgraded. Save money by going FF now, rather than build up a crop kit, then selling it off again later.
IMO this is probably the best answer given in this entire thread. In the beginning I fell for the glass before camera bit and it was total BS. When I finally moved to ff it was exactly what I was looking for and it made my L and non L lenses even better.
I'm not going to suggest any cameras that you didn't ask about which so many here will do and have already. IMO if the 5D2 is in your reach go for it, however if it isn't then go for the orginal 5D. It's still an incredible camera and even though I have the 5D2 I still use my 5D all the time.
The orginal 5D and 50 1.8 combo can create amazing photos> just look in the 50 1.8 and 5D threads. I use that combo all the time when I want to travel light with better IQ than my sl1 can offer. I pack my sl1 and 40 when I'm taking snapshots only or even my lx7.
Just know that using the 5D/50 1.8 combo has it's limits if you are trying to shoot in the dark. The 50 1.8 will struggle to focus, but in my case that's when I use my 50 1.4 to handle that.
The 5D is a great investment without breaking the bank and you don't have to baby it. You can get out and use it >even bang it up (if that happens). If you don't like it you can still get your money back when you sell it. Just think you're buying a $2500 camera for $600-500. It's a win win! Also canon will still repair the orginal 5D if you need to send it in. Win win again!