Ninja 400r, Ninja 650r, SV650... more than fast enough. You should want to ride to enjoy riding
Foolish to think that you need to start on the fastest bike in the segment. Especially seeing that you've never ridden. I'm a 33 yr old stocks guy... My preference was a Ninja ZX6... Glad i didn't. Bike is built for a track. You'll take a long while before you'll be able to even come close to pushing this bike anywhere near it's limit. No matter what... your first bike will not be your last. Look for something for 2-3 years.
All bikes are fast, it's just how fast do they get up to that speed.
Listen, i've been riding for 1 month on a Ninja 400r. I too didn't want to start on a 250 bike and have to upgrade next year when i outgrew the bike quickly. I'm happy that i bought the 400 instead. Powerful enough to go fast, managable enough to learn on. Its not actually about the power or speed. It's about the power delivery. A 4 cylinder 600cc bike is crazy fast. A 2 cyclinder 650cc bike is also fast, but no where near as fast as the 600cc!
My very first ride on a street was about 2 hours have taking delivery of the bike and riding in a parking lot. I was coming south on Pape avenue doing about 30km/h and saying to myself, "damn... this is fast with everything else around like cars and people and buses... I still don't ride on the DVP because it's faster than i thought it would be to maintain high speed for any length. And the wind! WIND SUCKS! Scariest thing yet. Especially on the highway. I've ridden in rain and wind, and would much prefer the rain any day. Wind will blow you right across the lane.
After taking the course the following weekend of getting my bike i felt a lot more comfortable. You have to put in the time to get used to the bike. I personally think the two month restrictions for the M1 are absolutely essential to the learning experience. It's the right amount of time.
Insurance on my bike is $950yr, the 650r was 1380, and the ZX6 (same category as your GSXR) was 2450. (you pay this in 4 installments over the summer months, not 12.)
Do yourself a favour... relax.
Definitely take the course. You learn a lot, and who cares if your drop their bikes.