I have actually found, after using the 3.5# connector for a while, that I prefer the stock 5# connector. The difference between the 5# and the 3.5# connectors is BARELY noticeable, and I actually find the 5# has a much cleaner/crisper break. The 3.5# feels to spongy/springy.
I had the extended slide release, and found though it felt nice, I really never used it. You should slingshot the action closed anyways. Don't want to cause excess wear to the notch in the slide, otherwise the slide will start slinging forward when inserting a magazine with less and less force. The stock release stays much closer to the frame, as not to get caught on anything, whereas the extended release has a little gap between it and the frame increasing the potential of possibly catching on something.
I would say, stick with the stock connector, and stock slide release. one improvement I WOULD recommend though, is a Vickers Tangodown Extended Mag Release. It stocks out a tiny bit more then the stock release, and is shorter than the Glock extended release (so it doesn't get depressed accidentally in your holster). The edges are also rounded with is much more comfortable/less sharp than the Glock version. It's not essential, but I much prefer it.
I was the same way when I first got my G17. I wanted to mod it, and did with all those things. I have since found, that Glock did their homework. They come this way stock for a reason (minus the mag release of course

).