Not everything needs probing as the System Scanner will work without probes and will scan within 5AU of your ship in about 30s. So you can warp to planets/celestials and pick up anomoly (?spelling) exploration sites and warp to them. You won't be able to scan down WH's or other Cosmic Sigs based sites.
Probes can now be reused (thankfully) and also are stackable now in your hold when they've been used. Reused probes don't expire or have any kind of lifetime outside of when they're deployed. You can also reconnect probes should you get disconnected or change system without recalling them. Probes last for about an hour.
You'll need 8-16 probes (8-16 of both types if you can use the Deep Space probes @ Astrometrics V) - 16 will give you a set of spares should something go wrong.
Deep Space Probes have a max range of 1024 AU & a min of 32AU (iirc), Core Probes have a max range of 32AU & a min range of 0.25 AU.
With practice it's possible to scan down a site within a few minutes - and a good guide on how to probe can be found:
http://www.eveonline.com/ingameboard.asp?a=topic&threadID=1007848A related spreadsheet that's very handy for finding specific types of signatures (using Target Size) is:
http://www.eveonline.com/ingameboard.asp?a=topic&threadID=1005459Anything that can be probed has a target size (so WH's leading to a highsec K-Space from W-Space has a size of x, a WH leading to 0.0 from W-Space has a size of y, a mining site has a size of z, etc) and the spreadsheet is handy as it allows you to relate signature "target size" to Signal Strength based on skills/modules/implants & the type/range of probe you are using. This allows you to scan & home onto a specific type of signal.
This works well generally but has a few issues when you have a lot of signatures to select from with overlapping Target Sizes.
I'll writeup an additional little guide on using probes when I have an approach that I feel comfortably works well. The main aspect I'm trying to cover is when you have lots of signatures found in a system. W-Space systems have a LOT of signatures as all content is based around exploration - by a lot the minimum number of signatures has been 20; with the avg for a simple system is 30 - and for a complex system: 50 signatures (max signatures has been 61 so far). This make is difficult to pick up a specific type of signature (