How do I measure a fork for suitability?
The overwhelming majority of modern road forks are designed for 10mm axles and 100mm-width hubs. (Since the hub width is the important measurement, it's the inside measurement between the dropouts which should concern you).

After you've ensured that the wheel sizes are the same (700c), the largest concerns are the axle-to-crown measurement; or very nearly what you're measuring as "the dropouts to the brake point", the steerer length, and the fork's rake.


Axle-to-crown. As you've surmised, changing this will modify the angles of the bike. Increasing it will rotate the bike back, slackening the head and seat tube angles.  Reducing it will steepen them.  Unless you've got a particular desire to change the handling of your bike and are willing to work out the geometry (see Damon Rinard's article for starters), it's advisable to keep it as close to "as-designed" as possible.  3-4mm is a minor change. 20mm is significant. It will also reduce the range of tire sizes you can run and most likely require new brake calipers, as they typically have only 20mm of total adjustment.  I don't actually see the axle-to-crown measurement on the fork you have linked.
Steerer length. This is the amount of steerer tube from the top of the fork crown.  On the fork you linked, the steerer length is listed as 250mm, with the top 130mm threaded (leaving 120mm unthreaded).  You'll want to remove your current fork and measure the steerer tube.  If it is longer than about 220mm (rather long) it probably won't have enough room for you to install the headset and get everything threaded on - you'll need a longer fork.  If it's less than 150mm (rather short) you may not have threads far enough down the tube to tighten everything, so you'll need to get more threads cut at a local shop.
Fork rake. This is the distance that the axle is offset from the centerline of the fork.  Changing this dramatically will also change the handling of the bike, so try to stay close to what you have now unless you want to work out the maths. You can measure it by having a friend hold the old fork vertically and then sighting down the steerer:
 


There are lots of resources to learn more about how fork rake affects handling, Dave Moulton has a good introduction.  The fork you have linked doesn't show a rake measurement.