How much gluten will set off somebody's celiac disease?

I am celiac. Ideally you should clean your entire kitchen, clean out your silverware and utensil drawers and wash all utensils in the dishwasher. Wipe all surfaces and sinks with bleach wipes. Scrub all pots and pans, to remove gluten films then wash in dishwasher. give all dishes to be used a run through the dishwasher.

Off limit items are seasoned pans (cast iron, or porcelain), earthenware, pasta pots, strainers, toasters, cooking stones, wood spoons or utensils, cutting boards, blenders and crockpots.

To avoid contamination use fresh mayonnaise, mustard, peanut butter jars, etc.
Do not use any ingredients such as sugar that may have been contaminated with flour from use while baking.

Because you are not familiar with ingredients that contain gluten, use only pure ingredients if you are cooking for your celiac guest.

Avoid spice blends.

Also see: Unsafe Gluten-Free Food List (Unsafe Ingredients)

For most celiacs, it is any trace of gluten. That means that you don't want something to touch gluten and then touch the food a celiac will eat (example: a butter knife used on toast and then double dipped back into the butter will contaminate the butter). My gluten-free friends have suggested that they are better judges of ingredients, as well, as gluten hides stealthily in things like chicken broth injected into inexpensive chicken brands.

You can probably keep your gluten products in the kitchen, just make sure when making gluten-free food that everything is clean.

Apart from the official recommendations (20 PPM), this is also individual. You should hear with your guest what applies for this person. Some needs a very strict clean environment, while others tolerate some minor contamination.

Clean cooking

Normally, you don't need to remove everything with gluten from your kitchen, as long as you keep products with gluten separate from the gluten-free products you plan to use in your gluten-free cooking. You should also not bake anything with flour when having gluten-free products in the open. After baking/cooking with gluten contained products, you need to be thorough in cleaning up in the kitchen afterwards. It would be best not to bake anything with flour when you friend is in the house, because flour dust will float around in the air. But just having the flour packed away in a cupboard or drawer will normally not be a problem.

Practical tips

Bread meals can be a challenge, but as long as you keep some basic rules, this will go smooth. To be sure nothing you serve to your guest have been contaminated, you should buy new food to be sure butter, spreads, meats, jam etc. are clean. You can put out a mug with some clean knives and spoons that you can use to take from the jar/box, and lay it on the side of your plate before applying with your own knife on the bread.

I beleive the Celiac Foundation's definition for "Gluten-free" is having less than 0.06 parts per BILLION of gluten. Yes, I'm serious. For example, just removing the coutons that have already been added to a salad won't do the trick. You have to never have put the coutons in the salad to begin with. (this comes from experience at a restaurant that supposedly knew what gluten-free meant).