"What's the longevity of a surface I plan on using this for about 6-7 years"
Well...it really depends on how much you'll use it. I can only tell you my personal experience:
- Surface RT: I have one pretty much since launch. It'll be 5 years old in December. It still works. Of course, it's slow as hell and barely does anything useful and I haven't used it for the last 3 years except ocasionally if I go on achievement hunting on the Xbox (it serves as a guide). However, the original Surface RT unit I had died after the first 6 months.
- Surface Pro 3: I also have one since launch (It turned 3 years a couple of days ago). It still works fine. The battery, however, goes away quickly so I now barely use it unplugged. But that's pretty much it. However, I had to get a Spectre X360 to replace the Pro 3 for mobility. Because I needed a portable device and the new Surface Pro is way too overpriced for the little that it offers.
However, again, my original Surface Pro 3 unit also died within the first year (well, in this case it was the keyboard connector that died).
So...if you take REALLY good care of it, it *can* last you for 6-7 years. But quite honestly, I wouldn't count on it. The Surface devices are pretty but they are most definitely not the most reliable. And I certainly wouldn't count on them lasting you that long with daily use. Furthermore, the older the device gets the more likely it will be for Microsoft to NOT support it even with hardware repairs. If for example in 4 years you have a problem with the device, it's very likely that Microsoft won't fix it for you, even if you pay them. Because the thing was discontinued already and they don't actually repair devices, they replace them with new units.
I would go for something else. The HP Spectre line is a good one to give a look at. And if you're in the US or any country that Dell covers, their offerings are also worth taking a look at.