Hi, I hope I can provide some info.
What are the pros 'n cons between canvas, leather, heavy cotton, and other materials in shooting apparel.
Canvas
Pros: rigid, good as a support, better esthetic (for some people).
Cons: will become dirty quick, especially the white ones (I suggest for not using white/bright colored canvas on the upper part of the arm that hold your buttplate, frontside stomach near supporting elbow, and upper back near neck); somewhat hard to clean; somewhat long break in period.
Leather
Pros: short break in period, good at conforming to body position(s), better esthetic (for some people).
Cons: maybe a little worse than heavy canvas for supporting the body, may rot and bleed if exposed to water (some people shoot in the rain with a jacket on).
Clarino/suede
Usually they are used on the frontside stomach near supporting elbow to provide grip, and on the upper back to provide comfort.
For the top (pricey) models, special materials (in Kurt Thune's they are 1.5mm heavy canvas, 0.9mm soft canvas, leather, and clarino) are used on specific body parts/regions. You can take Kurt Thune Expert model as an example (
http://www.edinkillie.co.uk/thune/evolution.htm). I suggest that you download the measurement on that page - it contains a sketch that tells where each material are located on the jacket.
For the basic (less pricey & sophisticated) models, it seems that the general concensus is to use a combination of heavy and soft canvas.
What should I look for when ordering glove, boots, shooting jacket and pants by email.
Is it just like ordinary cloth or should I look into another kind of measure.
You should ask for a measurement (for the jacket and pants) first, anyway usually the dealer will automatically give it when you order a well known brand (such as Gehmann, AHG Anschuetz, Sauer, Kurt Thune, Mouche, etc). But if you want a lower price, you can ask for a standard size (it basically is a "not so made to measure" jacket/pants). For the glove you can measure your hand on some website (I forget the address). And for the shoes you know you foot size, don't you?
Oh and by the way, it has been mentioned in this forum by someone before (and I agree) that you shouldn't take a bigger size jacket/pants (for that unexpected day when you are gaining weight or in fear that it will be too tight), because jackets will stretch and conform to your body as time pass, and don't fear to move the buttons (as long as you don't break the rules).
Hans