Pressure problems thinking the pipes are too small
	
	
		Our house is a 3.5 bath with a sink and dishwasher in the kitchen as well as cloths washer in the laundry.  The house is a 2 story older farm type house.  The main coming into the meter is 2 inch.  What happens after that is it turns to a 3/4 for about ten feet then everything branches of that to 1/2.  
One bath room is on the second floor the kitchen, laundry room, a full bath and a half bath are on the main floor and a full bath is in the basement. Would it help to replace the existing 3/4 with and 1 inch and the 1/2 with 3/4 as far as I can without opening walls.
Also I am thinking about using PEX Vs copper but I am not sure about it.  Is it really safe or am I just being paranoid?