i' was in the same field as you, wondered the same thing about 2 weeks ago. the answers i say because i feel more confident now as a rider, but i went medium cost and recommend paying for as much as you can affort (in terms of quality)
street-go two piece leathers, also i ride with a leather jacket, always a back protector, and always (unless 1 or 2 miles) riding boots, and gloves in the 100+ range. what you wear also depends on what you mean by street riding. communute...or race but on the street? if you wear jeans buy the kind with knee and hip pads, or do like i do and by thick jeans, buy strap on skateboard knee pads (tougher than most people understand, spend some time on a half pipe and you'll know) and sow in some football pads for hips.
track-go one because all tracks accept it. as for brand, most that you find are good, but the cheepest ones are a bad call. for example tecnik makes a good suit, but only their top end on, their cheep ones are poor. Joe rocket you can get away with a $800 dollar suit. Icon tends to have higher prices all around. Comfort? comfort/fit varies from person to person. regardless of comfort makes sure the elbow, knee, hip, and back pads in your suit are snug and don't move. when tring on you suit crouch like when your're on your bike, thats how you'll use it and that's where you'll decide what is comfortable. suits $850 and up.
design is you're choice, by that i mean look. see above on the company brands.
Sidi is a great boot (i even bought one), you ought to buy a boot with ankle support that won't let it roll. your boot price range should be $260 and up
gloves are odd, big difference between the $50/80 and the $100 ( i settled their because for a one time fall which ='s good enough). between the $100-150 not a big difference, between the $100 and 180+ a big difference.
yes i over did the question. but just for the record there is no such thing as a coincidence, you make fall at 100mph in the cheapest gear and run away laughing, or you may fall in $3000 worth of gear that saved your to a life of a broken spine. nor is their such a thing as probability or odds. sorry i alway over do things