Left Crank Arm & Squeeky Brakes

Hello,

Had to change my inner tubes the other day, so I did that but then couldn't get the wheel back on due to me fiddling with the brakes, so this closed the pistons on my discs.

Little did I know they were closing so I prised them back but fluid went everywhere including my pads.

I succesfully bleeded the brakes today and I have strength back in them, however it's now making a god awful squeek which vibrates when I'm nearly stationary, is this because I mananged to get mineral oil on my pads?

I have Shimano BR-M486's

Also when cycling my left pedal was making a creaking noise so I thought i'd take it off, grease it up and put it back, except I believe when they fitted them at the place I bought, they cross threaded it, so now I have a knackered crank arm.

I believe i've seen the ones I need, but there £30 or so squid, which isn't a lot except everything seems to be going wrong recently and if I can i'd rather fix it cheaply.

Can I get any old crank arm, as long as it's the same length and square tapered (which mine is - All though i've seen online some pics say it's squared but it actually looks like a star to me)

btw, I am a noob, but my bike for the last 2 years has just worked fine.

It's probably due for new pads all round anyway, but I seem to be having problems finding a brake spacer for it, unless anyone knows where I can purchase one from.

Thanks!