3km is approaching the limit of 5.8GHz equipment with reasonable size antennas and typical WiFi radios. With some of the best equipment you can only get ten times that distance with some caveats.

900MHz can easily go 3km, and much much farther. 900MHz is used for a wide variety of devices for this reason, so there's a good level of background noise. This might be a problem, especially if your neighbor has a 900MHz phone or similar (not a popular frequency for phones these days, but people hold on to technology for a long time too). I would avoid this frequency unless you're in the middle of nowhere (which you aren't). The 2.4GHz spectrum has worse problems with this, our microwave at work blasts 2.4GHz (I'm sure it violates FCC something or other, but nobody really cares as we have 5GHz WiFi). 

Wireless link frequency choice (900Mhz vs 5.8Ghz) for 2-3km distance
I have three floor joists that have approximately 1/2 inch hole in them less than 2 inches from the bottom. Is there a recommended fix or approved method to correct this to meet code?  These joists are in excellent condition otherwise. Someone drilled through them years ago to run cable through. There are other holes above 2 inches on other joists.
