choose the bracket that it fits into, e.g. 700x18-25 Race 28 will fit

By contis, i assume you mean the Continental brand tubes. Your tube size would be Continental Quality Road Inner Tube:Presta 42mm 700x18-25 Race 28 .The first measurement looking at what i typed above, is length of the stem. The second is diameter of tube and 3rd is width of tubes. The 700C isn't any actual measurement but a common name for 622mm diameter tubes. Just follow the tube diameter and tyre width when buying tubes. And of course shradler or presta type tubes.

Any 700 x 19 - 23C tube will work. If you have standard width rims, a valve length in the order of 42 to 51 mm is good. Tubes come in many weights, so pick the one for the intended application. As an example, the one you need to fit in an ultra compact saddle bag may be different to the ones you generally will ride on.

Also check whether you want a presta or schrader valve first.

You will see plenty of tubes marked 700 x 25 (usually saying 25C), though they usually fall within a range like 700 x 18-25, or 700 x 25-35, which is because the tube would actually fit any wheels/tyres within those ranges. 700 refers to the diameter of your wheel (mm) with a tyre on, while 25 (mm) relates to the width of the rim. There are some suitable tubes held here http://www.wiggle.co.uk/continental-quality-long-valve-road-inner-tube/

No

Yes, they do. They're 2 part Presta valves and you can unscrew the inner part. At least the ones I bought last time did have!

This is the height of the tyre from the shoulder of your rim

Outer tyre diameter, it corresponds roughly to inch. 26 is common for mountain bikes, 28 for older road or continental city bikes. Go by ISO number or google "bicycle tyre size" when unsure.

Metal

Schwable do multi fit tubes that does both 700C and 27' and for me that would be your best option.

Stick to Schwable as they tend to be good though prefer Raleigh's Puncture Resitant tube especially if you are using non-puncture resistent tyres. Using a VAR tyre tool and a bit of patience and the tubes will fit.

Tubes are usually made in China, some in Idonesia and Tiawan. Michelin tubes were at one time made in France and now the tyres are made in Tiawan so the tubes will probably be too.

Go for a 25-32 as the tube will be sitting chilled out in the tyre not stretched and stressed if you were to use a 18-25. This should reduce your punctures to virtually nil. Stretching the rubber makes it very thin and weak just like a balloon!

Try Sheldon Brown http://sheldonbrown.com/tire-sizing.html#width

Sounds like you've got a 700 C hybrid tyre 17 mm rim width (i.e. 17/25.4 ~ 5/8 inch).

Try a Vittoria Zaffiro Pro Folding Clincher Tyre