Don't worry about your stay at Amaravati, it's going to be lovely, they're lovely people. Very laid-back place, no stress whatsoever.
If you travel to Berkhamsted (instead of Hemel Hempstead) you find a Tesco supermarket very near to the station, where you can buy some cheese or dark chocolate to take as 'dana' (donation). They're allowed to eat those in the afternoon. Also there's a taxi point right outside the station (about £9 the ride) but you can walk from there, if you're clever enough to find your way (I'm not!).
Enjoy your stay