welcome! That's how started, lurked around here for a while (still mostly what I do lol) but now I have had a hypermotard for 2 years and it's well down the road of modifications lol. Good to have you here, hope you end up getting your hands on one.
As for reliability it really comes down to the maintenance that was done on a bike, especially older ones. So if it looks like it has been well taken care of, and if they have the documentation to back it up you should be fine with those bikes. I don't think the 03-04 749's are known to have any outstanding reliability issues.