Second factories are not especially unusual. Normally in 1v1 it will be a plane or gunship switch. Occasionally someone will build a vehicle or tank factory if they started with bots, but that is quite rare. Switching factory is a good way of attacking your enemy without them having counters ready, so building up a few units for the attack so you get a big attack in before they get those counters ready is often best.

Or give you access to new area's of the map to further grow your income (i.e. high hills or islands)

Seen the replay, it's a slow, porcy game imo.

That was well cast too. I think you missed a bit of what was going on with venom69. I think the lack of assist from the Rectors on the top right was because he was trying to make the Vehicle Factory on the left ASAP. The Storage (it holds both metal and energy) may have been built to stop excess or perhaps to plop turrets. Although I do agree that the Storage was a bad idea.

The Impalers top left was actually a very good move. He had a well fortified position on the doorstep of OldGhostStalker but it was off to the side so not that useful in a direct assault. The Impalers force the fortified position to be dealt with because otherwise the entire base is lost.

Also OldGhostStalker has an Infiltrator, that is how the commander became stunned.

This was a fun cast. I was really hoping for that trollcom to turn the tide. But at least it had a flashy death. :)