I did #2 on 12" centers. 36x48, 4" deep with cross beams dug in. Took 34 yards to do. Been up for almost 3 years and no cracks. it was done by local pros in day and I don't regret the bill one bit.
There is a channel on YT called R&R buildings. They pour pylons and use some special bracket they insert into the top of the pylons to lock them in, then when the build the walls, the raise them as a unit and bolt the posts to the brackets. They seem to know what they are doing. I like their work methods. Worth a look.