So if my laptop has wifi turned on, and it sends probe requests to a router that has 2.4GHz network, will these probe request be in that range?
Of course. The probe requests are meant for the access point , which is listening to a specific channel. Typically that’s channel 1, 6, or 11.
WiFi uses considerably less transmitting power (<100 mW) than cellular phones (up to 8 W). The radiation health risks are accordingly much lower to non-existent (in comparison to radiation from other nearby sources).
Some portable devices may reduce power even when actively transmitting actively when the connection is good enough, but there's no standard.
Q1: ... wants to send data to an exterior host (STA B), residing in different network
That's not possible via data link layer alone. The host needs to use a network-layer protocol like IP and direct the encapsulating frame to a router/gateway in between the networks (which has nothing to do with Wi-Fi). For (off-topic) consumer-grade devices that may be the ...
I don't think there is a general answer to this question without knowing what functions (besides Wi-Fi) does Wi-Fi AP have. Here are some anchor points for the answer, so they do not exist in comments.
Border router can be different things, and depending on that, there are different ways deviced decide how to forward packets. I found these references which ...
The router has two interfaces— one on each network. Each host is configured with the default gateway set to the address of the router interface.
Traffic to the other network will be sent to the router, which will forward it to the destination.
Note that the Ip packet has the destination address of the host, and that never changes.
A frame is only transmitted once and you can capture it only on the transmitted channel, once. Only if there are multiple copies of an original frame should you be able to capture (mostly) identical frames multiple times.
Wireshark doesn't suppress/filter multiple identical (or mostly identical) frames.