First thing to do is drain all gas and dispose of it. It is dead. You say you have drained it, but the tank should come off anyway and it needs to be cleaned it thoroughly, as there will be sediment in it.
The fuel lines can be removed at both ends and cleaned. A carb cleaner spray with a long nozzle will do this easily. . If this is done, hold the lines vertically to let them drain and dry quickly.
Tires and battery were "almost new" four years ago?
If the battery has not been kept charged, it will have died, or will be very close to that point now.
If the bike was stored outside and in the sun your tires are worthless and MUST be replaced. If it was stored in a garage, the tires might still be OK, but they will have hardened over time, as that is what ALL tires do, whether in use or not. The best usage life is about five years from date of manufacture, not date of purchase.. More is certainly possible, but performance drops with each year and if you drive on old tires as though they were brand new you are almost guaranteed to lose the bike in a corner the same tires would have handled easily when new.
Tires have a limited life span: they start aging as soon as they are born from the mold. They all have the date of manufacture on the side, and you should check this. Here is a guide for this
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=11
Remember, please, NOTHING on the bike is more important than your tires.
BEFORE turning the engine the first time, remove all spark plugs and pour in about an ounce of light oil. Some will recommend different brands, but a 5-30 or 10-30 will do nicely. Let it sit overnight before turning the engine over, and then do it with the plugs still out. Place some cloth above the holes when doing this to catch the oil as it is blown out. .
Let the engine spin without compression for a few seconds, at least. The oil you added will supply lubrication to at least the top rings and the piston walls before the engine can get oil pumped into the area. It is done because any oil that was there 4 years ago will have become so thin as to be useless and friction will be quite high when you first turn the engine over.
Remove and clean the carbs. You might consider having this done professionally, as the expense may be worthwhile.
At home it can be done, with one of several carb cleaners They are used as a bath, by soaking the carbs in it, then blowing them dry with compressed air. Read the instructions carefully, before starting.
This will be essential as the old gas will have largely evaporated, and the balance turned to mud, or close to it, and it will clog the tiny passages in the carbs. Leaking gaskets should be replaced, but check the hoses for cracks, as they also age. If you have a fuel filter, replace it.
Brake fluid should be fine, but check all hoses and connections for leaks or swelling.
Buy a can of spray brake cleaner and use it generously. Put down paper to absorb the run-off. Turn the wheels while still wet as the brake pads may have become stuck .