Let me start by saying install your suspension before you do anything with wheels.
When installing new wheels/tires, you always want to maintain the overall diameter of the wheel that came on the car from factory, or at least stay close to it. Reason being that venturing too far off will drastically change your speedometer/odometer accuracy. When moving to a bigger rim, say from 16" to 17", the profile of the tire (second number) must get smaller to compensate. For example, my car came with 205/60/16 tires stock. When I moved to 17" rims, the 60 became 50 to maintain the closest overall diameter to stock. Search tire calculator on here or google and mess with different tire sizes to see what I mean. What it does is allow you to put in your stock tire size and show it in one diagram, then putting in your new tire size next to it and showing that in another diagram...thus allowing you to compare what profile you need to go with to maintain overall diameter.
Some people do not maintain overall diameter (usually because they're lowered more than 2.5" or slammed), and go with a smaller profile that makes their overall diameter smaller than stock. For your drop, 2" is decently mild and going smaller than factory diameter will give you the "small wheel look". While I'm on your drop, you do not need a camber kit for a drop 2" or less. Yes you will run a tiny bit of camber, but as long as you rotate your tires when you would anyway, you're good.
As for what tires fit what rims, every rim width can accommodate a range of tire widths. But there is always a maximum tire width that can fit on a rim. You can learn alot about this by spending some time on Tirerack.com. When you select a rim on there, they will give you a recommended tire size for that rim. Just to give you an idea, here are some typical tire widths and rim widths...for a 6.5" wide rim, typical tire width is 205 (but could be 195 or 215)...for a 7" wide rim, typical tire width is 215 (but could be 205 or 225)...for a 7.5" wide rim, typical tire width is 225 (but could be 215 or 235). The numbers in parentheses are a range, you can actually go lower than those for different results. You can go wider, but going too wide on a rim will make the tire "balloon", which looks bad.
And here are profiles you would go with relative to different rim diameters...for a 17" rim your profile should be 50 to maintain close factory diameter. For an 18" rim your profile should be 40 to maintain closest factory diameter. Again, these can vary at the person's discretion and they depend on the section width. However, with a 2" drop, this is what would I would recommend for you. For the 17, you could actually get away with 45 I think though.
Contrary to popular belief, your tire width will affect your speedo/odo readings as well. The profile number is actually a percentage of the section width, so they are interrelated. I just learned that a month ago lol
Anyway, just do some reading on there and you will learn about this. Also, go through the member's ride threads and see what tire sizes people have put on what rims, and you'll get an idea (you'll need to look up the rim width for some). For what you are going for, I am not going to get into tire stretching, I wouldn't worry about that for your first set. And tire stretching with a 2" drop would look awful.
Spacers are used for pushing your wheels outward toward the fender to make the face of the rim more "flush" with the car.
EDIT: I'm sure someone else can comment on the concept of offset better than I. But you can learn about that on TireRack, and if you search on here, someone linked to a great offset calculator that gives great visualizations.
i had 18x8 wheels on my car for like a week but it was only the rears bc i didnt have tires on them if you wanna see what they would look like with a mild drop in the rear and the tires i think were 225/45/18's
