you have exactly the same iteniery as I do.

it is MUCH cheaper to buy Eurostar ticket from eurostar.co.uk. remember even if you are traveling one way only, buy a round trip ticket with at least 2 night stay. I just bought a ticket for $90 per person. and they sent the ticket to me here in Los Angeles when I booked online.

as for Paris to Rome, see the other thread. it costs less booking from sncf. but it is a little more complicated.