There's loads of information out there regarding the topic. While some people choose to not be productive in their responses, the fact is the answer to your questions are out there and can be found with a bit of searching. While I don't personally have one, by best friend here does and I've helped him nuermous times with parts and the build aspect for the car.
In regards to your questions:
1-How much did it all cost you in the end? So like, how much did you pay for your kit, paint, install etc.?
For the entire kit with the wing (Fenders, skirts, lip, diffuser, GT wing), you're looking at about $4,600-$5,000 depending on who you buy it from and assuming you're buying authentic products and not replica items. As far as everything else, it depends on who you take it to for paint and installation. Install is relatively easy and can be done without much hassle if you have a helping hand. There are threads and info regarding how to cut and install the kit. There's even a template to you to determine where to cut the original fenders/quarter panels. If you can manage to do the install yourself and only require a third party to do the paint, you'll probably be in around $5,500-$6,000 from the get go; assuming who you take it to does quality work. That's also assuming you have the tools required to install the kit.
2-Do I need anything in particular with the kit when I buy it? I plan to get a new exhaust when I get the kit, but also some new rims and wheels too, but is anything else NEEDED?
Besides rivets/screws to bolt the kit on, nothing else is really NEEDED; but when I say that, that means that the kit would fit on the car without adding extra modifications. HOWEVER, you will DEFINITELY WANT to add proper size wheels (and spacers, if applicable), in addition to some type of aftermarket suspension to fill the extremely large wheel arches and some type of aftermarket exhaust to fill out the large cutouts in the rear diffuser. It's not a requirement to make the kit work, but it will look extremely awkward without it.
3-How is rear visibility with the wing? If possible, could one of you guys hop in your car and take a pic of your rear view mirror
I can't help you with this as I haven't been in one with the rear wing, but I would imagine it's not that bad. I imagine it would be similar to the likes of the OEM STI and Evo wings. While they can be seen in your rear view mirror, they don't really block a large amount of your vision out of the rear window.
4-Any place I should take it to in particular? I'm from CT, so I don't think there are too many well known body shops here
I would go into the regional section of the forums and ask in there simply because anybody who isn't from or familiar with CT will not really be able to help you. I'm from CA and currently live in OK and cannot even begin to tell you what is up there in CT, as I've never been. Hell, at this point, I'll just assume that it's a fictional place and doesn't even exist.
Just to humor you on this, I'll price out an estimate now:
-TRA Widebody w/ GT Wing: Approx $5200 (shipped price)
-Enkei RS05RR Wheels (18x10/18x10.5): Approx $2400
-245/35 & 265/35 Dunlop DZ102 Tires: Approx $850
-5x100 to 5x114 Wheel Adapters: Approx $250
-Stance SuperSport Coilovers w/ swift springs: Approx $1400
-Stance Rear Lower Control Arms: Approx $500
-Project Kics Lug Nuts: Approx $250
Just with everything listed above, you're in about $11,000. That doesn't included costs for installation or paint if you have somebody else do it. For me, I'd install myself and I have a friend who paints so I'm covered. I simply pay for supplies which is a few hundred bucks.
Keep in mind this is just an estimate and the overall cost can be higher or lower. You can buy more or less expensive wheels, tires, suspension components, lug nuts etc.; but the fact is that the Rocket Bunny route as a whole is going to run you around $10,000 total for authentic items.