1) would it be ok if i were to cut the tail pipe right after the muffler and turn it so it comes out from the side?
Check with local laws, if not worried about the laws then why not? When idling you may smell exhaust, not good.
2)is the brake fluid in the master cylinder supposed to be dark green, almost black?
It should be clear. More than likely no one every flushed the fluid.
3)I cnt tell how old my battery is because the sticker is bleached from age and heat, it is an autolite 96. so how long might it last more?
5 yrs on average, How long will yours last, no one can answer that