Extending my WiFi. Boost the signal, or buy a repeater?

I've been doing some reading and I see that there are aerials (https://www.amazon.com/Cisco-HGA7S-HighGain-Antenna-Connectors/dp/B0002F3E9M?tag=computerworld0e-20) and signal boosters (https://www.amazon.com/Hawking-HSB2-HiGain-Signal-Booster/dp/B0009MYSHU/ref=pd_sim_sbs_147_2?ie=UTF8&psc=1&refRID=M2DX5PR83MGQ8QPT76HZ) that can be used to extend my WiFi, but aren't there limits to how powerful these signals can be broadcasted? I'm sure if you put enough power into these transmitters I could get a WiFi signal to be sent several miles, but I would guess there are some legal limitations perhaps?

Perhaps this is difficult to answer, but should I buy anotehr router that acts as a repeater, or is the general go-to solution to get a satisfactory WiFi signal to get one decent router and replace the antennas?

I also have a quick question about using several access points for the same wireless network. Let's say I have two routers all part of the same network and I stand in the middle of them, which router will my device connect to? Do I risk my device toggling between the two of them, connecting, disconnecting, connecting again if the signal strength from both of them is about the same?