I have 2 Harleys, and never had an oil leak. My garage floor is clean with no spots. Although I have had some older ones that did, I think it is mostly myth and old legends. Just check the bike, and look at his garage floor. Even the old ones that leaked were still a hoot to ride, and most people just put a piece of cardboard on the floor to catch the residual drip. The leaks were never significant, just annoying, requiring washing more often to keep the bottom clean.
Both of mine are carb, but I would not hesitate to go EFI. It is just a lot more reliable, and a lot less maintenance. My cars, trucks, and Polaris 4 wheeler are all EFI, and I love them. It is true that they may be a little more complicated to work on, but they are so reliable, that one rarely if ever has to work on them, or even touch them. Anything from the last 10 years will likely be EFI.
I have one rubber mounted Harley, and one solid mounted. I much prefer the rubber mounted, because the vibrations are less prevalent. I don't see how that affects the weight more than a couple of pounds one way or the other.
I tend to stay away from high mileage bikes, just because there are so many low mileage ones out there to choose from. Now my Dyna has a lot of miles, and I would not hesitate to take it across country tomorrow, but it has been well maintained. I will also admit that it is more likely to have a problem now than it was when it was newer, just because things wear out with age and use.
When buying a used bike, you never really know how it was treated or maintained. You can get clues from checking it out and asking questions, but will never know for sure. You are basically taking the chance on a used bike for the savings you get from buying it new. In my experience the depreciation savings are worth the risk.
In the case of Harleys, you also have the opportunity to get a lot of chrome add ons for free that the owner bought but will never get his money back from. Just avoid the ones that have been stripped down, hacked, bobbed, or chopped up, unless you really like it, and you really get a good deal.
Good luck, and happy hunting.
1999 Honda Rebel CMX250C
2003 Harley Sportster 883 Hugger
1998 Harley FXDWG Dyna Wide Glide
ALL IN! GO TIGERS!