It might seem overwhelming at first, but all of this can be done if you have patience and $. If you don't want to do the work why did you buy a $250 dollar bike? Not trying to be a jerk, but maybe you would have been better off buying a runner? Anyhoo, most of the stuff listed is pretty easy to fix, but you won't get it done in a day or a week, unless of course you spend a bunch of time.
So going down your list here are my thoughts
Carbs everyone has to deal with
The seat can possibly be fixed? Or buy another one off ebay
There are many OEM style replacements available
Rear shocks are found new or used, perhaps a junk yard, or evil bay
centerstands are nice to have but not neccessary, I use a motorcycle jack that I got from sears on sale for $70
Tires again are expensive, but you kind of need them to ride
you can get stock handle bars/ grips used cheap
Surface rust can be taken care of pretty easily with steel wool and some soap, or get a replacement
Exhaust isn't very cheap used or new, but can be had
you can adjust the brake lever, not too hard
tanks suck, but almost everyone has had to do some work to them
mirrors can be had pretty cheap on ebay, as can sidecovers
All of these jobs can look at one time to be overwhelming, but take them one at a time and with a little patience and some dough it can and will be done.
