There are really only two bar diameter standards these days, 31.8mm and 35mm.

Make sure you find out which one your current bars are!

Almost all forks nowadays have a 1 1/8" steerer tube at the point where the stem attaches.

There are a few forks still around with a 1.5" steerer but it's quite unlikely you need to worry about this.

You can always measure your current stem/steerer if you want to be extra sure. (1 1/8" is about 28.5mm)

This is very tough for us to answer but somewhere in the vicinity of your fork offset is generally a good place to start.

Remember, a longer stem doesn't really make up for a bike that is too short for you (and vice versa). It affects other things as well, namely handling.

We refer to this as "stack", and it's 38mm on all of our stems. (Apart from the direct mount of course.)

As much as possible! Your steerer should only be about 3mm shy of the top of the stem. (Just enough for the lip of the top cap to clear)

Pro tip: the steerer goes entirely through the stem and sticks out the top by about 3mm. Then use a headset spacer on top. This is how we build our bikes here at Chromag HQ.

You can read the full user guide here, but making sure everything is clean is a great start.

Follow torque specs, and make sure the faceplate has an equal gap top and bottom.

Handlebar markings only get you so far, if you want to be super accurate, get out the tape measure!

If something is creaking it's almost always due to dirt and dust. Take everything apart and clean. This would also be a good time to inspect for damage.

If you have a crash and tweak your bar angle, for the love of god loosen your stem when setting them straight. It also goes without saying to give your bike a good look over after a crash, especially the front end.

It's never a bad idea to replace your stem bolts each year (you'd be surprised how corrosive sweat is). We sell replacement bolt kits at a very reasonable price.