I didn't buy ME1 until it was about a year old for the 3rd person reason. You can easily get used to it. It doesn't hamper shooting at all. Well with a mouse. Your gun is only drawn when you're in combat. Outside combat you just walk around normally.
As for dialogue, there actually aren't that many options. You usually can be a good guy or a jerk. I don't think that really comes into play until the second game with the Paragon and Renegade. Usually dialogue options, and squad choices, lead to who lives or dies in certain circumstances (like once per game, not all the time), or who shows up in a certain position in the game. There's really no extraneous dialogue that doesn't make a difference. There is a mission in ME2 that ended up being never discussed again, even though they made a big deal about it. That was because the original writer (Drew Karpyshyn) left after that game.
I would get the first game, which should be pretty cheap, and see if you like it. It actually has a pretty self contained story so even if it's not your thing, you won't feel like you missed the rest of the story by not playing the other games. Other than that, it's got one of the best stories (except last 5-10 minutes of ME3 IMO) of any video game and great characters. You actually want to talk to the characters in this.