Also what is the view of the Eurostars at Ashford like?
It really depends what you want. There's a good view of the Medway Viaduct from Cuxton Rd A228 near junction 2 of the M2 but it's very loud. It's within 30 mins of Cuxton station The closest you can get to a Eurostar at speed is probably the down platform and footbridge at Westenhanger station but it's pretty well fenced as you'd imagine. HS1 at Ashford is on a viaduct to the north of the station and is above platforms 5/6. You can hear and see Eurostar but it's not a particularly good view. There's a good view of the Channel Tunnel terminal from the Pilgrims Way / North Downs Way at White Horse Hill it's about 2.5 miles from Folkestone West.
I know where that bridge is but I've never been on it. The problem with HS1 is that the line has lots of noise attenuation and security barriers. South of Ashford the service is quite sparse in the off Peak. I guess Ashford station itself would have more of interest tbh.