I love this restaurant. I love the staff. I love the food. I understand that people could somehow not like it, but I feel the need to address concerns for those that might be deterred via an instruction manual. :-D
1) Walk in and smile at anyone there, greet them!
2) Head to the counter in front of you and grab an appropriate amount of menus and find a table.
3) Once you decide on menu items, go up to the counter, ring the bell, and order.
4) Bring a book or people you like to talk with and the time will seem short, you could also encourage those bewildered and fearful souls that wander in (I have met some amazing people here by breaking the invisible walls around my table).
5) Enjoy food that you will not get anywhere else, don't expect it to be a carbon-copy of a dish you had before.
The people that are serving you at Van Hahn are not employees, they are either nuns or volunteer laity from the temple. If you show them kindness, you will get it back from them, they are not financially obligated to treat you like the lord or lady of Downton Abbey. They do not work in the service industry, they are contributing to a humble cause. The place is humble as well, it would not be consistent with their lifestyle to waste money on a fancy bathroom remodel... you will notice most decor is repurposed like the rack advertising wine that they don't serve.
I would recommend the soups (pho, hue's spicy noodle, and sweet and sour are my rotation), the sushi rolls, potato rolls, chicken nuggets (when you're feeling trashy), green papaya salad (papaya is cut fresh, so it will take a minute), house special (my absolute favorite), spicy spare ribs, kung pao chicken (mmm, mmm, good), and really anything else you might want. Word of advice though, fried rice dishes are not what you think they are... the rice is brown and steamed, everything else is stir-fried.
The last thing to address is the mock meat level of the cuisine... I would recommend that you put on your thinking cap and infer from the description, which dishes will have the appropriate proportion of mock meats to vegetables.