If you use a well sterilized thief, infection is not something you need worry about. It never hurts to be mindful of resterilizing your bung/airlock before replacing it either. A your yeast will also create a competitive environment for any other organism that may infect your brew. People have brewed beer for a long long time; way before Pasteur, van Leewenhoek, or Koch were born. RDWHAHB!
Your OG will depend on a lot of things. Being a newbie myself, I don't know it all. However, I can venture an educated guess that the solute content of your extract, your specialty grains, hops, and the amount of water you use to bring your batch to its final volume will all factor into this. How long has it been in there? Can't hurt to take a reading now and track the change!
In my brown ale, I used a dark and an amber extract. The OG was somewhere around 1.062, but I was using an unconventional style of hydrometer -- long story.
Being somewhat impatient also, I am going to keep testing the gravity of my brown for a while before I bottle it. I'll shoot for 4 weeks, but the longer you leave it in the fermenter, the longer you give the yeast time to clean up the off-flavors created by the fermentation process. Let it sit on the yeast cake for a while and try to keep your mind on other things!
Hope this helps!