Honestly, if you're using an Extract brew, you don't have to worry about it.
Testing for OG is important for finding efficiency and knwoing your beer is done and calculating ABV
Leave your beer in the primary for 3 weeks and you should be fine. For extract brewers using a hyrometer is just practice. Also your OG is calculate before you start fermentation, if you dont' test it before fermentation, all you can test then is the 3 day rule to see if fermentation is done.
As far as getting it out of carboy, a wine thief will certainly work, for me though I saved 5 or 6 bucks and just got a turkey baster.