How many brake lines?

That depends on why you are replacing one line. Typically there are four steel lines, one going to each wheel, but there are variations on the master cylinder design. A few have all four steel lines leaving the master cylinder. If a rear line rusts out and starts to leak, it makes sense the other rear line is just as rusty and should also be replaced. The front lines are better protected from salt and water so they cause less trouble. They most commonly rust near the end where they attach to the rubber flex hose right by the wheel. Often it's not practical to try to replace an entire line from the master cylinder to a front wheel. Instead, cut the line in an accessible, rust-free area where you can slide on a fitting, then make a double flare. From there, install a union and a short length of line to replace the rusted section. For best success making the double flare, do that in a section of line that is straight. If you try to straighten a section that had a bend in it, the flare will form off-center and may not seal. This video will show how to make your own lines.

https://youtu.be/sO43p4ZFUiM

Please run down this guide and report back.

I would think you have a clogged brake line, either the rubber ones or a steel line.

You should be able to bleed all wheels, best way is to use a compressed air bladder that fits over MC resivour (sp?).