I totally agree with the idea of buying more truck than you think you will need. With my first fiver I was fine, even though I was shocked after weighing it to figure out we had added over 2,000 extra pounds to our total combination weight. The new fiver was slightly heavier and now we are right at our limits so I have to constantly monitor my weights and keep things adjusted.
As far as having slides and having problems with slides, I wouldn't have a fiver without opposite facing slides in the living room and at least one slide in the bedroom. We can get to pantry, fridge, bathroom/shower, and bedroom without putting slides out.
The thing about problems with slides is you have to take care of them. Most manufacturers will tell you they should be adjusted once and awhile, plus gears should be properly lubricated and inspected on a regular basis. We take it a step further and keep our seals coated with 303 plus we never run the slides in and out without being level. Our brand claims you can walk on top of your slides but I personally would never do that.
Lastly, you have to pay attention to your tires. Many, if not most fivers and TT's come with tires that are rated generally for the delivered weight of the unit. By the time you load all the "stuff" in them and hit the road you could very well end up with underrated tires which will fail. You almost have to go over the scales and know your exact weight (loaded and ready for travel) before you can be confident you have the correct tires mounted. Just because that new shinny rig came with those new shinny tires doesn't mean they won't blow in the first 1,000 miles.