I am a big fan of the M&P. All of mine are series 1 and I have not shot a or even handled the 2.0, but everything I've read about the 2.0 says that it has improved the 1.0.
Like Dogmush said, you can probably find a used 1.0 pretty cheap. The difference between the 1.0 and 2.0 aren't that great. Just a couple of ergonomic changes and some fine tuning.
Unless you are a dedicated shooter who like to practice, I recommend staying away from pistol optics. Learning to get a good sight picture (finding the dot) takes a bunch of practice. If you are already a really good pistol shooter, the transition won't take long. If you only shoot occasionally, you'll need lots of practice to get comfortable. Also, RDSs require some maintenance whereas iron sights really don't. Batteries die, the sight shuts down, the zero may drift. All of these problems are easy to overcome, just be aware they are there.
The downside to the 1.0 is that it wasn't offered with a slide made for optics. There are a few special models that have optic cuts, such as the M&P CORE, but there aren't many of those. I had to buy a CORE in .40 and then buy a 9mm barrel to get what I wanted. I think all of the 2.0s are optic-ready.
The factory mag holds 17. There are plenty of companies making longer/extended mags if you want more. And if you are looking for performance upgrades, I highly recommend Apex Tactical.