Front hard break lines on my 2010 4Runner have rusted pretty badly. No damage to the break lines, but rust is pretty significant.

It looks like the long upper line that connects to triangular connector (Toyota calls it Union Way) is in good shape except for break line screw. Everything that is below connector has a lot of rust. If I mess up long break line screw, it will become a bigger job than I want to do.





Left and right upper front lines (47316 & 47314) are still in good shape, but there is a lot of corrosion on the screws. I will most likely need to use Groove Joint Pliers to get the screws off.



I was thinking of:

1) Cleaning upper break lines nicely and coating with POR15, and changing only the lower hard break line that goes from the break hose to the caliper.

2) Taking a more risky approach and using groove joint pliers to get small upper hard break line screw off of triangular connector, and then changing the entire assembly (small upper and lower hard break lines, and break hose).

How far do you guys think I should take it as far as changing hoses and lines?

You have some ugly crud going on. First I would scrape/wire brush all the loose stuff off, then if you decide to replace any lines give the fittings a good soaking with liquid wrench or similar for a few days before starting to remove/replace. Or clean up the area good, sand down the lines and coat as you mention.
Be sure and use brake line wrenches when you work on them.

I discovered the same thing with my new (to me) '99 SR5. I was just going to slowly accumulate all the lines I want to replace and do at least most of them all at once because I want to bleed my system as few times as possible. Your lines look like they could use a little bit of sand paper and that should remove most of the rust. After that some paint would make them look good as new.