Each of the two temporary structures (one in each room) will need to mimic the section of wall that is being removed. So if the jack poles are resting on a single bottom-plate and are holding up a double top-plate, then jack poles 16" on center are called for. If something more substantial than the double top plate and single bottom plate are used, then fewer jack poles are required. In the extreme, it'd take only two jack poles placed 6ft apart to hold up their own temporary 4x10 header. The first floor's floor will need similar support in the basement.
I'd build the temporary support structure using lumber that I could use again somewhere else.
All that is assuming the ceiling joists are perpendicular to the wall in question and that the support structures are placed close to the wall in question.
If instead the ceiling joists are parallel to the wall in question, then there must certainly be a 2nd flr wall that is on top of the wall in question, in which case all the temporary support structures will need to be installed up on the second floor.
Personally, though, my choice would be to do it like this, without shoring up ...
0) pick through the pile at the lumber yard for straight 2x10s
1) open the wall on both sides
2) install the king and jack studs
3) notch the top of the studs on one side to let in one 2x10
4) install the that 2x10 onto the jack studs
5) shim between the cut tops of the studs and 2x10
6) cut off the stud ears (produced by the notching) that are on the side
7) nail off the 9" wide rippings of 1/2" plywood filler
8) install the second 2x10 onto the jack studs
9) nail off the header
10) remove the shims
11) remove the old studs
I called an engineer and paid for his evaluation of the wall. It's not load bearing. Realized that I left out some basics about the house.
This house is built on a raised foundation with cripple walls attaching the floor joists to the foundation. The metal post is attached to the fireplace foundation (which is independent of the houses foundation). There is no foundation (just 3 feet of empty air) underneath the wall I want to remove. The header is just oddly sized.
The header does not connect to the beam.
From a sheer wall perspective he was not too concerned, given that the total amount of wall I want to remove is pretty minimal compared to the rest of the house.
Best Answer
You absolutely need a header. From what I see there, doubled 2x10s should do.
The wall was apparently built like that because 12' studs were expensive or unavailable, so they built a standard-height wall and then extended it. That probably wouldn't fly with modern code due to the effective hinge point in the load transfer path.
None of that changes the fact that you need to support the framing above the opening as normal. In your situation I'd lay the header in above the existing double plates, then fill down below them to your opening height. This approach retains the lateral integrity of the wall as much as possible.
Be sure to temporarily support the framing above. There are a few good posts on that here if you need advice.