Crappy Bike Brakes - and Paint vs. Old Steel - Please help me fix my friends bike

I’m in need of a creative solution. My friend bought a lousy, worthless tragishamockery of a double-suspension mtn. bike off eBay after his good Giant was stolen.

The p.o.s. never made it a mile. Now I’m fixing it up, on the cheap-cheap so his parents can use it at their Florida condo (why they just don’t go and buy a brand spanking new Target Magna for $60 is beyond me, but I don’t own any condos).

Anyway I’ve taken the derailluers both off and adjusted the chain length to single-speed it and now I’m trying to make the caliper brakes work. I was willing to pop for new brake cables - but I don’t have any tubing and I don’t want to buy any.

So my question is two fold - how can attach the brake cable to the caliper brake in a meaninful way. Please not that the original bolts have crumbled (they were a screw with a hole for the cable and a nut to tighten). Part two of this inquiry is how awful is it to run brake cables without the use of tubing? Can these cables rub up against the frame with no damage to themselves?

Help a guy out -

Oh and a simple question: What’s the best way to get paint off a steel frame?

Peace