I've seen your pics, impressive.

To make $ on siding, s&f, gutters,,,

there is a fiberglass wood reenfocing product I have seen used on wood tower bases , I am not even sure you need that



I think it's a barn , I would cut 6x6 to go on either side of the post that is there and get them in snug on top of that concrete wall that can help carry your load as insurance and run some threaded rod through to tie all that together with nuts and washers on each side.

then something to stop that from rotting any more , wire wheel out the loose stuff and treat it so it doesn't degrade more.
maybe something like an asphalt fence paint

or make your own so asphalt fence paint

get that wood sealed down a foot or so below grade and paint it up to the top

it sort of looks like that top plate and beam are not treated lumber might paint all that also.

well thats my thought on making a barn work for a bunch more years without dropping a fortune on it.

I think I would do one more thing , dig that down around a foot all the way along and lay a drain tile and cover it all with stone so you get drainage and keep that dry as you can for the future.

I just put another post beside the rotten ones and connected them together.

You know what? I was thinking that you could put some blocks between the concrete and bottom of building. That would keep it from tipping over.

Not sure if you have room, but Techno metal posts work great in applications like your situation.

also wouldn't hurt to tar from a foot below ground to about 2 feet above

water soaking into concrete and freeze thaw is hard on it.

This is a very real possibility and it makes things a real pain.