If this all goes ahead, you will also need to consider where you're going to put all this stuff on the train. Of the train companies at the stations you mentioned, Greater Anglia, c2c, and First Capital Connect trains have next to no storage space for anything larger than a carry-on and East Midlands Trains are little better. None of these offer checked luggage (which is commonplace in the US). Eurostar is much better and has a luggage van and checking facilities. This sort of journey may lend itself better to a hire car.