Finally some progress to report guys.
Lots and lots of work.
Been downstairs, trying to prep the area for a new floor, and a new set of stairs.
The new permanent wall is all framed up carrying the load of the new studio.
I replaced one rotten corner post, tore up the floor above to get the joists off the beam, then took out a large chunk of the beam and extended the post above it all the way to the floor.
Went through about 6 charges with the sawzall, but she zipped right though everything like butter.
The impact driver was amazing to have for all the timberloks and lag bolts.
See PICTURES:

Took out the door and the trim. Looks pretty mangy. THis will be covered up with siding eventually and the door relocated to the wall on the right.
The stud wall is holding up the studio, in place of the beam.
There are little blocks above the header to hold up the old joists.

Yay! This sucker basically came out in my hands and was one of about four pieces that looked like that. Utter garbage.

DIdn't budge an inch. You can see that 2X6 to the left just in case, but nothing moved at all. I had to chop that beam out of there to extend the post all the way up.

The new post! I had to chisel for about an hour up at the bottom of the beam to try to get it more square. I gave up and it still isn't anywhere close to square. We put an angle iron on the top, and on the bottom connected to our wall sill. See other picture...

This is really the only thing connecting this half of the barn with the other.
I'm going to put some more 2X6 in the gap between to get another lag or two into it. That 2X4 you see behind is holding up the double 2X4 header which basically isn't doing squat, maybe holding up the smallest angle of the roof.

Took no chances on bracing this guy. With a nice 2X6 scab to the floor with 4 timberloks, and a 2X4 on either side, screwed into the protruding old floor joists. Luckily one of the joists was sistered onto the post, so I think that helped.
I put a 2X6 on my car jack to take just a tiny bit of the beam upward, then we put in the supports.
It took awhile to cut out that "Dutchman" joinery with the sawzall, but it came out quite nice.

I'm really very proud of this work. It's basically seamless. It's got only three 6" timberloks in it now, because the fourth was splitting the post.
I think we'll put some steel across the seams, and an angle iron or two down at the bottom into the stud wall.
The big cavernous opening is the result of my taking the floor OUT.
THere's still another post to contend with on the other end of that beam, but the rest of the beam is held up with a bunch of temp supports.
Just to be very safe I went into the studio and put a double 2X6 temp post under the end of the beam in the studio.
I really should get another picture of that Dutchman joint. It's sweet. Luckily we had a big chunk of post sitting around that pretty closely matches the other one. Up close they're a bit different though.
The bottom of the post is anchored to a 2X6 PT, which is sitting on the cement. I'll probably tapcon that down just for grins.
I used pinch sticks to measure the length of the post (perfect scraps I had laying about from ripping extension jambs on the big window), then just cut it a kerf long and pounded it hard into place with a big maul. If you tap the post now, it's a high pitch and feels like it's carrying a lot of weight. Job well done.
Much more work to go on this sucker, but it feels great knowing that I'm doing it right, and this damn barn will stand another few hundred years.
By the way, looking at the inside cross section of the beam I sawed off, it actually looks pretty good with a lot of good meat left. Still, though, I'm doing the right thing for the barn. The whole setup was so cobbed.
Once I severed it with the sawzall, and zipped a few nails t hat were toenailed through the joists into the beam, I gave it some hard whacks with the maul from above, and it dropped right out. So far have taken out maybe 5 feet, and about 20 feet left.
Will have more pictures soon.
The spacking on this outer wall upstairs was the first bit I did, unfortunately BEFORE I learned how to do it properly, so it looks like **** and is way too think. Some sanding down the road, and a few more coats...
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FUTURE PLANS:

You can see the old stairs right in the foreground, way too step for code.
The red lines outline the proposed new stairs, with a raised landing at the bottom. This shortens the length, thereby creating more of a "safe" landing up at the top, clearing my studio door by about 5 feet.
I think I might just leave that room vaulted to the top, I think it looks sweet.
The window is unfortunately right on the middle, and thereby can't really serve as a window or as a door with the stairs there. So, might have to basically rip that wall out, try to salvage the relatively new prime cedar shingles.
Or, just try to be careful and do it from the inside. Maybe try to make the doorway where the window is now. I think it would be nice to have a little window at the bottom of the stairs, though.
The red arrows point to the floor joists sticking out that were resting on the beam. The plan is cut all this out right flush to the level of the header on my new wall. I built the wall so that it's 1/2" behind the one above it; in other words, once it's drywalled, it will line up perfectly with the outer wall of the studio. The studio partition wall there is 2X4, where the one directly below it is 2X6.
Soon I'll get some pics of the rest of the upstairs and how this picture relates to the entrance of my studio.
Peace.