Disclaimer: not an engineer, but I’ve built a house and squatted half a dozen.

Questions:

• how much load might it be supporting (what is the porch made of?)
• how high and long is the concrete beam and approximately how many decades old?

Ideas:

• don’t remove woodwork until you have investigated the cracked concrete, removing anything that comes loose without striking; determine for sure if the concrete is fully compromised or partly so

• if concrete is only partly compromised, one method would be cutting off the compromised layer and casting a filler, but you should re-calculate the load bearing ability of the beam as if the filler was nothing

• after this you have a concrete that can be effectively supported from below

• if you use a jack and a pillar, prefer a mechanical (not hydraulic bottle) jack, people sell and rent such instruments for temporary support, it’s a steel pillar made of 2 parts that you rotate against each other to extend

• your plan to offer support from the center and replace the framework from sides makes sense

• if water if a frequent visitor there, use treated wood