I would say 300hp par for the course with the base kit and no other mods. This is what you can expect with any of the base Centrifugal kits as well. Pulleying it for additional airflow and adding further breathing modifications (exhaust, intake, heads, etc) later on down the road will yield better results.
Kenne Bell supplies VERY detailed instructions with all of their kits and anyone with moderate automotive knowledge shouldn't have an issue installing it in the driveway over a weekend. Your best bet would be to get a couple of your wrench-head buddies together, with a case of beer and a couple of pizza's early one Saturday morning and go to it.
The kits themselves are nearly silent. You'll most certainly hear an increased rush of air entering the inlet side when you put your foot into it, but otherwise it's fairly quiet.
For starters, I would bolt up the kit alone and perhaps just address the transmission for now. A decent shift kit and a transmission cooler should be your first priorities. Leave the rear gears alone for the time being to see how you like it. Like I said before, a lower (numerically) gear set isn't mandatory for good performance with a Positive Displacement blower like it is with a Centrifugal. You may find yourself happy with the stock gears and as such will save yourself several hundred dollars for their purchase and install that you can put towards something else in the future. Like say a set of heads that’ll really wake things up!!!
If it were my money and you already planned on swapping intakes, I would get the kit designed for the GT40 lower and buy the matching lower intake manifold for it. That way, if you do choose to upgrade the heads later on down the road, you’ve now got an intake with competent breathing capabilities to match them to. You can save a little money now by going with the standard intake design, but later on if you choose to upgrade the rest of the engine, the lower intake is going to serve as the bottle neck of the combination.