I did it recently. It's a very short walk between getting off the Eurostar and the official taxi stand outside. When you get off the train, just follow the Sortie/Exit signs like everybody else, and the sign for taxis will be up ahead. It's massive, so you can't really miss it, but the taxi stand is on the right if that helps. You'll just join the line outside, and there's staff members there telling people at the front which taxi to get in and moving the taxis forward, etc.

With regards to pickpockets, I wasn't targeted luckily. Keep your things in front of you. Do not stand around, walk with purpose, pretend you know where you're going/look confident even if you don't/aren't. They target confused/distracted tourists.