Flushing is not a "routine" procedure for a normally maintained engine. If you have an engine that has not had regular oil and filter changes then flushing may help clean it up but generally such an engine is already damaged.
As far as flushing the cooling system, same story. If the coolant has been regularly change then there is no point. If it'...
My first bike had been sitting around for a few years, in addition to getting it running I'd advise making sure it will stop. Brakes have a tendency to seize if they aren't used, so I would inspect front and rear and test them thoroughly.
The carb may be gummy but I'd see if some carb cleaner will do the trick first, rebuild it only if you can't get it ...
Since you are a beginner then in the interest of safety you should get an experienced rider to try the bike. They may come up with things that dont show up in a static test.
We in Britain are not allowed to ride bikes over 125cc until passing a test. I guess theres a reason for that. So starting out on a 1200cc is remarkable.
All the best
So, apart from setting the baseline as per the other answer, you should get the service schedule and follow it.
Also, given the age you should check things more often. Oil, filters, chain, suspension joints etc
After sitting for so long and at this age you should:
Replace all fluids and filters.
Replace the tires
Check the wheel bearings
Check and either clean and lube the chain or replace it. (I don't recall if this has a chain or a belt. If a belt, inspect and adjust it.)
If the clutch cable is damaged, replace it.
Check the inside of the fuel tank for any ...