For the turn signal problem, does this happen at idle and full throttle? If so, You might need a new flasher relay, this is located behind that plastic rectangle in the front of the forks and can be purchased at any yanaha retailer or compromised with another other than the origional with maching specs though. If this only happens at low speeds, you might need a new battery because the bike can't power the ignition, head and taillight at idle, if the batterys fine, suspect the charging system, it might be bad or weak.
Oil type, my manual says for 2 stroke, any yamalube, 0.8 qts of it.
For engine case oil: I like to use synthetic 10w30, start off by putting in a quart of it, and check with your pinky finger evry quarter of a quart after, if you feel it, your good to go.