I think someone born in the 1920's would be able to answer why it's 2T.
I was wondering why for a Korean your English was quite good
(I have a few Korean friends).
There are a few other people too that sell the billet power valves, so spend a bit of time researching them.
The forum will have a workshop manual you can download from there, it will have all the torque settings for bolts, and you'll be able to get an idea of the sort of tools you'll require. you'll basically need an assortment of screwdrivers, allen keys, sockets and spanners, torque wrench, impact driver, screw extractors (if you snap bolts).
PV servicing is covered in the forum over there, when you get there, do a quick search. Once you get the PVs out, definitely replace the screws with cap heads (I think M4x10 or some small size), so you won't have to deal with rounded out philip head slots.
Other checks you should perform? If you're paranoid like me, I start with fresh fluid so I have restarted the service history: New brake fluid (check pads and rotor wear while you're there), coolant (check hoses while you are at it), new gear box oil (check no metal shavings or "shiny" oil). Keep using the same two stroke oil the previous owner was using.
Do you know how many k's the bike has done on the top end? If not, factor in a rebuild ASAP, or do a compression test, both dry and wet.
Also check the lower shock mount on the frame, if the bike has really been abused, these have been known to fail.
You're lucky that most of the GSXR stuff (late 90's) will bolt in as a replacement, or with a bit of work the K series GSXR stuff fits in
