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
The cement lintel would be for brick walls, right?
To determine the size of the lumber you should use, you have to consider the load it will be carrying (the roof, snow, attic...) and the distance spanned - the whole 12' if I am reading your question right.
This picture
is from a site that has lookup tables to select the company's engineered lumber products but it illustrates the calculation well. Here is a lookup table provided by a county in Maryland:
http://www.aacounty.org/IP/Resources/HeaderSpanTable.pdf
It's a simple table that one would assume is based on standard structural engineering for the snowfall typical in that locale. (Which is not a lot of snow!) You can see that in that locale, even two 2x12's won't fly for a 12' span. You'd have to move up to engineered lumber or a box beam or etc.
So you're seeing spanning 12' is a whole different animal than putting in a doorway or window. To be safe, you could
1) hire an architect / structural engineer
2) hire a competent contractor and let them handle it
3) if the job has a permit, ask the inspector
(If you go routes 2 or 3 it might ultimately wind up back at 1 depending on your local regulations.)
Best Answer
You can attach the joists (studs) directly to the sleepers. The point of using a top plate (not actually a header) in the design you shared is probably to...
Regarding your second question, you could probably screw the angled studs directly to the vertical studs, but you'd lose any load-bearing benefit from joist hangers, and you'd lose the load-distributing quality in the horizontal ledger/plate. You also eliminate the possibility of putting drywall or sheathing behind your climbing wall without dealing with all those framing penetrations.