If this pole footing is defective in resisting horizontal load, then the retrofit should have at least 3 ties
Why? Curious as to the code you are referencing.
What Ron said.
What process is being used? SMAW, GTAW, FCAW?
This is the depending factor. Also the position.Longer welds are better than bigger welds FYI.
What do you mean one element needs to be designed for yield? Are you talking about the welding of the base metal?
I would find your natural frequency and see if you need to apply dynamic loads. If you're rigid (>30Hz for me) don't worry about it. FYI Iv'e never designed a bridge, just grandstands ect.
Why not make the support a gravity connection only? Are you resisting shear at the connection? If you put bolts there, I'd say it will take uplift loading no matter what you put between the base plate and the wall.
You need a barrier. Period. Wood is not going to cut it in the hole unless its sealed. I would think about using BASF or SIKA epoxy grout to embed the post. No moisture is going to penetrate that.