The "mode C veil" is always around class B airspace only(30nm arc). If you don't have a transponder then its a no go.
Class C airspace does not have a mode C veil, you can transit or land at a class c airport with prior notification if you have no transponder. VFR-VFR seperation does not exist in the USA. However, VFR-IFR seperation does exist.
VFR a/c can not fly into class E airpace when below the meteorological mins stated in the FARAIM (similiar to australia meteorological mins). This means that the only time they are in class E airspace is during VMC DAY OR NIGHT.. therefore SEE AND AVOID.