Just about everyone in my circle of Porsche friends uses the Motive Power bleeder, which is available from our host. And we use 25psi as our pressure and have never even come close to blowing out a reservoir. I have no idea where that advice is coming from. If you go 15 or lower, you barely get the fluid to flow. Now I am in no way advocating 90psi, LOL, but you should be fine with 20-25psi.

I use 10 psi with my motive. Works fine.

To flush, I use a turkey baser to remove most of the old fluid from the reservoir. I find that then removing about 170 ml at each cylinder does a 100% flush and I have a bit left in the can.

With a helper, I manually bled my brakes tonight.

I used $8 Valvoline Dot3/4. I used about 1 bottle.
I drained the blue and replaced with clear.
That made it easy to see when the fluid was purged.

How long can leftover brake fluid be used, if you close the cap on the bottle?
What exactly is the shelf life risk? It's it's capped tightly, moisture will not get in.
Will the air in the bottle ruin the fluid over time?

I know the method is
1) open bleeder
2) press brake
3) close bleeder
4) release brake
(repeat)

I did not see air bubbles getting sucked into the hose when I told the helper
to release the pedal with the bleeder still open. So, I switched to:

1) Open bleeder
2) Press and release brake repeatedly until fluid is clear
3) Close bleeder

This was much faster, and seemed to work exactly the same.

1st, you want to insure you do not damage the MC by placing a block of 2X4 piece of wood behind the brake pedal. I made a notched block to prevent it from falling off while my helper pressed the pedal.

Bleeding:
1. Press quickly and raise slowly several times to build pressure
2. Release Valve no more than 1/4 turn and quickly close.
3. Repeat 3-6 times, until you see ZERO BUBBLES, shine a flash light on the hose to insure no bubbles are present. Prop the hose upward so you can allow the bubbles to go upward not back up to the caliper.
4. Top off reservoir, move to the next caliper.

A week later after driving her hard, repeat to insure calipers are free of bubbles.

Flush:
1. Open the valve and allow the fluid to come out on it's own via gravity method ( this slow ) until new fluid shows up. Again prop the hose upward to insure zero air bubble re-entering the caliper.
2. If inpatient, have helper pump the brakes very slowly. Speed it not your friend here.
3. DO not allow reservoir to go empty.

As far as storage, once bottle is open it will absorb moisture right away at the micro level. I put mine in a zip lock bag with some rice. The theory is the rice will absorb the ambient moisture in the bag and help keep it out of the fluid. Who knows, maybe too much OCD but it would not hurt, it saved my water logged cell phone :D

I Googled shelf life of opened brake fluid.
2 year shelf life

It reads "sealed" shelf life, no?

I guess it's a moot point, b/c whatever is left over isn't enough to do a full bleed.
The only other time you need a little bit of fluid is to top off after brake pad wear.
But, that fluid will just sit in the reservoir anyway.
I'll probably just toss the bottle to make shelf space.

Oh no, keep it for the next flush, as the primary dump fluid and chase with new fluid.