Check the specs, but your current gas line will probably be fine. Same with your electrical - an all gas range only needs a 110 outlet which you presumably have with your current range. Most likely you'll be able to just swap the new range into place. Your major expense will be the ducting for the hood and any electrical that it needs. If this is all you're doing, you probably don't need a GC - just an HVAC guy to install the hood.

Thank you Weissman for the info.

It depends on how much BTU your new range will demand. I was advised to increase NG pipe diameter from 1/2" to 1" because I went with a high BTU Capital Culinarian. 3/4" would have been fine but the plumber said might as well do 1" to be sure. Capital engineer I spoke to on the phone thought it was overkill, but in doing the math using charts I found on the Internet backed up the plumber's advice.

learned this the hard way when I upgraded my grill and plumbed a NG line to the grill. Went with 1" line so that I could upgrade my range at some point in the future. Not cheap (had to run the line across my whole house) but i'm so glad I did it.