Right now I'm in the middle of remodeling my basement and right now all my plumbing is wide open and would be very easy to replace or upgrade.
the ? I have is the main water line is 3/4 copper pipe then it goes though a 3/4 water meter then its down sized to 1\2 copper line that runs to the water softener and the hot water heater. then after that its goes down to 3/8 line.
the house was built in 1962
Right now I have a very young family/growing. In years to come with two girls there will be alot of water being use.
How is your water pressure and volume right now? If you're on public water, that should not change much in the future, and if you have a Presssure Reducing Valve, you may be able to increase your water pressure if necessary later without any replumbing.