I am not sure how helpful this will be, if you have not already booked a package with a direct train to Disney included, do consider 'independent travel'. We do this and find it easy, cheaper and convenient.
Book your hotel/ticket package with DLP direct, then book the Eurostar direct with Eurostar. that way you'll get tickets from Ashford and will have reserved seats etc.
We get any old train direct to Paris - best price we have ever achieved is just under £60 return for two adults (total - not each!), more usually its £29.50 pp each way so about £120 all in. Then change in Paris, go from GdN to Chatelet then hop on the A line RER to MLV.
Think its about 12 bucks for the trip (each) and takes 40 mins.
Ok so you're travelling alone and not on the Disney direct train, but you get much more choice in train times and can extend your time in the parks if you wish. Trains are less crowded, quieter. Although not direct and you have to do a bit of metro/rer on your own, its only 2 hours to Paris GdN from Ashford so even with a 40 min trip to get from GdN to MLV, you don't lose out too much. I think its worth a bit of extra hassle factor for the increased choice and decreased cost.
(I have travelled the disney direct service before, so this isn't totally uninformed! - but, only once, in 2000).
As for car parking we often do this (we live in Kent) and its safe, secure, and about £12 per day. remember you pay for part days too as well so a three night stay in the car park is in fact five days' worth of charges.
HTH
EK