Replacing/upsizing galvanized main line

[jml]

Hello, all. I've got what is apparently a galvanized main water line in my crawlspace, and I just found out that it's majorly corroded in some spots (but fortunately it hasn't ruptured yet). There are unions at either end of this run and it switches to copper at both ends (coming from the meter in the sidewalk and going to the shutoff valve for the house). This run is a straight shot that's probably 70' long, give or take, and I think it's 1", maybe a little larger. I'm either going to replace the galvanized myself or have it done, can someone set me straight on what is OK to use? This galvanized is currently sitting directly on dirt under the plastic moisture barrier, could I just replace it with copper (it is also a/the grounding point for the house, it's an old house and I don't know offhand if there's also an external rod or not). Barring anything unforeseen, I'm not planning on touching anything past the union going to the meter, which is probably 20' long or so and buried underground (as I said before, it appears to already be copper, or at least something non-magnetic). Would I see any benefit from going with a larger pipe for the new run? Pressure is OK overall, but I do get a serious drop if, for example, I flush the toilet and run the washing machine at the same time.

 

[Sylvan]

Normally when replacing galvanized it is customary to use non ferrous metal one commercial size smaller . reason being old timers knew galvanized would have internal corrosion and reduction in diameter